Use of per-connection MIMO support as basis for dynamic control of air-interface communication with dual-connected device

ABSTRACT

A method and system for controlling data split of a dual-connected user equipment device (UE) when the UE has at least two co-existing air-interface connections including a first air-interface connection with a first access node and a second air-interface connection with a second access node. An example method includes (i) comparing a level of multiple-input-multiple-output (MIMO) support of the first air-interface connection with a level of MIMO support of the second air-interface connection, (ii) based at least on the comparing, establishing a split ratio that defines a distribution of data flow of the UE between at least the first air-interface connection and the second air-interface connection, and (iii) based on the establishing, causing the established split ratio to be applied. Further the method could include using the comparison as a basis to set one of the UE&#39;s air-interface connections as the UE&#39;s primary uplink path.

REFERENCE TO RELATED APPLICATION

This is a divisional of U.S. patent application Ser. No. 16/949,776,filed Nov. 13, 2020, the entirety of which is hereby incorporated byreference.

BACKGROUND

A typical wireless communication system includes a number of accessnodes that are configured to provide coverage in which user equipmentdevices (UEs) such as cell phones, tablet computers,machine-type-communication devices, tracking devices, embedded wirelessmodules, and/or other wirelessly equipped communication devices (whetheror not user operated), can operate. Further, each access node could becoupled with a core network that provides connectivity with variousapplication servers and/or transport networks, such as the publicswitched telephone network (PSTN) and/or the Internet for instance. Withthis arrangement, a UE within coverage of the system could engage inair-interface communication with an access node and could therebycommunicate via the access node with various application servers andother entities.

Such a system could operate in accordance with a particular radio accesstechnology (RAT), with communications from an access node to UEsdefining a downlink or forward link and communications from the UEs tothe access node defining an uplink or reverse link.

Over the years, the industry has developed various generations of RATs,in a continuous effort to increase available data rate and quality ofservice for end users. These generations have ranged from “1G,” whichused simple analog frequency modulation to facilitate basic voice-callservice, to “4G”—such as Long Term Evolution (LTE), which nowfacilitates mobile broadband service using technologies such asorthogonal frequency division multiplexing (OFDM) and multiple inputmultiple output (MIMO). And recently, the industry has completed initialspecifications for “5G” and particularly “5G NR” (5G New Radio), whichmay use a scalable OFDM air interface, advanced channel coding, massiveMIMO, beamforming, and/or other features, to support higher data ratesand countless applications, such as mission-critical services, enhancedmobile broadband, and massive Internet of Things (IoT).

In accordance with the RAT, each access node could be configured toprovide coverage and service on one or more radio-frequency (RF)carriers. Each such carrier could be frequency division duplex (FDD),with separate frequency channels for downlink and uplink communication,or time division duplex (TDD), with a single frequency channelmultiplexed over time between downlink and uplink use. And each suchfrequency channel could be defined as a specific range of frequency(e.g., in RF spectrum) having a bandwidth (width in frequency) and acenter frequency and thus extending from a low-end frequency to ahigh-end frequency.

Further, each carrier could be defined within an industry standardfrequency band, by its frequency channel(s) being defined within thefrequency band. Examples of such frequency bands include, withoutlimitation, (i) bands 2, 4, 12, 25, 26, 66, 71, and 85, supporting FDDcarriers (ii) band 41, supporting TDD carriers, and (iii) bands n258,n260, and n261, supporting FDD and TDD carriers.

The coverage provided by a given access node on a given carrier couldalso be considered to define a respective “cell”. Thus, if an accessnode provides coverage and service on two carriers, the access nodewould be providing two cells, one on each carrier. And if two accessnodes provide coverage and service on the same carrier as each other,the access nodes would be providing different respective cells than eachother, both on the same carrier.

On the downlink and uplink, the coverage of each such cell could definean air interface configured in a specific manner to provide physicalresources for carrying information wirelessly between the access nodeand UEs.

Without limitation, for instance, the air interface could be dividedover time into a continuum of frames, subframes, and symbol timesegments, and over frequency into subcarriers that could be modulated tocarry data. The example air interface could thus define an array oftime-frequency resource elements each being at a respective symbol timesegment and subcarrier, and the subcarrier of each resource elementcould be modulated to carry data. Further, in each subframe or othertransmission time interval, the resource elements on the downlink anduplink could be grouped to define physical resource blocks (PRBs) thatthe access node could allocate as needed to carry data between theaccess node and served UEs.

In addition, certain resource elements on the example air interfacecould be reserved for special purposes. For instance, on the downlink,certain resource elements could be reserved to carry reference signalsor the like that UEs could measure in order to determine coveragestrength, and other resource elements could be reserved to carry othercontrol signaling such as PRB-scheduling directives and acknowledgementmessaging from the access node to UEs. And on the uplink, certainresource elements could be reserved to carry random access signalingfrom UEs to the access node, and other resource elements could bereserved to carry other control signaling such as PRB-schedulingrequests, acknowledgement messaging, and channel-quality reports fromUEs to the access node.

OVERVIEW

When a UE enters into coverage of an example network, the UE coulddetect threshold strong coverage of an access node on a particularcarrier, such as by detecting a threshold strong reference signalbroadcast by the access node on the carrier. And the UE could thenengage in random-access and connection signaling (e.g., Radio ResourceControl (RRC) signaling) with the access node to establish anair-interface connection (e.g., RRC connection) through which the accessnode will then serve the UE on that carrier. Further, the access nodecould establish in data storage a context record for the UE, noting thecarrier on which the UE is connected and noting associated serviceinformation.

In addition, if the UE is not already registered for service with thecore network, the UE could transmit to the access node an attachrequest, which the access node could forward to a core-networkcontroller for processing. And the core-network controller and accessnode could then coordinate setup for the UE of one or more user-planebearers, each of which could include (i) an access-bearer portion thatextends between the access node and a core-network gateway system thatprovides connectivity with a transport network and (ii) adata-radio-bearer portion that extends over the air between the accessnode and the UE.

Once the UE is so connected and registered, the access node could thenserve the UE in a connected mode over the air-interface connection,managing downlink air-interface communication of packet data to the UEand uplink air-interface communication of packet data from the UE.

For instance, when the core-network gateway system receives user-planedata for transmission to the UE, the data could flow to the access node,and the access node could buffer the data, pending transmission of thedata to the UE. With the example air-interface configuration notedabove, the access node could then allocate downlink PRBs in an upcomingsubframe for carrying at least a portion of the data, defining atransport block, to the UE. And the access node could then transmit tothe UE in a control region of that subframe a Downlink ControlInformation (DCI) scheduling directive that designates the allocatedPRBs, and the access node could accordingly transmit the transport blockto the UE in those designated PRBs.

Likewise, on the uplink, when the UE has user-plane data fortransmission on the transport network, the UE could buffer the data,pending transmission of the data to the access node, and the UE couldtransmit to the access node a scheduling request that carries a bufferstatus report (BSR) indicating the quantity of data that the UE hasbuffered for transmission. With the example air-interface configurationnoted above, the access node could then allocate uplink PRBs in anupcoming subframe to carry a transport block of the data from the UE andcould transmit to the UE a DCI scheduling directive that designatesthose upcoming PRBs. And the UE could then accordingly transmit thetransport block to the access node in the designated PRBs.

For each such scheduled transmission on the downlink and the uplink, thereceiving end (i.e., the UE or the access node) could determine whetherit received the transport block successfully from the transmitting end(i.e., the access node or the UE). For instance, the transmission couldcarry a cyclic redundancy check (CRC) value computed based on thetransport block, and the receiving end could compute a CRC based on thereceived transport block and determine whether its computed CRC matchesthat carried by the transmission. If the receiving end receives thetransmission and determines that the CRC matches, then the receiving endcould transmit to the transmitting end a positive acknowledgement (ACK)control message. Whereas, if the receiving end does not receive thetransmission or determines that the CRC does not match and thus thatthere was an error in the received transport block, then the receivingend could transmit to the transmitting end a negative acknowledgement(NACK), in response to which the transmitting end could then attemptretransmission.

In addition, for each such scheduled downlink or uplink communication onPRBs between an access node and a UE, the access node and UE could use amodulation and coding scheme (MCS) that the access node selects based onthe UE's wireless channel quality and specifies in its schedulingdirective to the UE. In a representative implementation, the MCS coulddefine a coding rate based on the extent of error-correction coding dataor the like that would be transmitted together with the user-plane databeing communicated, and a modulation scheme that establishes how manybits of data could be carried by each resource element. When channelquality is better, the access node may direct use of a higher-order MCSthat has a higher coding rate (e.g., with more error-correction coding)and/or that supports more bits per resource element, and when channelquality is worse, the access node may direct use of a lower-order MCSthat may have a lower coding rate and/or supports fewer bits perresource element.

To facilitate these and other operations while the UE is connected withthe access node, the UE could also regularly evaluate the quality of itscoverage from the access node and could transmit associatedcoverage-quality reports to the access node. For example, the UE couldregularly evaluate and report to the access node the UE's referencesignal receive strength (RSRP) and/or reference signal receive quality(RSRQ), which the access node could use as a basis to trigger handoverof the UE when appropriate. And as another example, based on RSRP,signal-to-noise ratio (SINR), signal-to-interference-plus-noise ratio(SINR), and/or one or more other factors, the UE could regularlyevaluate the quality of its wireless communication channel with theaccess node and transmit to the access node channel quality indicator(CQI) reports, which the access node might use as a basis to determinethe MCS to be used for air-interface communication with the UE.

In addition, when a UE is connected with an access node, the access nodemight provide the UE with carrier-aggregation service, where the accessnode serves the UE on a combination of multiple carriers at once, tohelp provide the UE with increased peak data rate of communication. Inan example carrier-aggregation implementation, the multiple carriers onwhich the access node serves the UE would define a “cell group”including a primary cell (PCell) or primary component carrier (PCC) andone or more secondary cells (SCells) or secondary component carriers(SCCs). To configure such carrier-aggregation service when the UEinitially connects with the access node or later, the access node couldadd one or more carriers to the UE's connection, noting the group ofcarriers in the UE context record and signaling to the UE to prepare theUE to operate accordingly.

With carrier-aggregation configured, the access node could coordinateair-interface communication with the UE on PRBs distributed across themultiple carriers. For instance, with downlink carrier aggregation, theaccess node could designate in a scheduling directive to the UE one ormore downlink PRBs respectively in each of the UE's component carriersand could accordingly transmit data to the UE concurrently in thosePRBs. And with uplink carrier aggregation, the access node coulddesignate in a scheduling directive to the UE one or more uplink PRBsrespectively in each of the UE's component carriers, and the UE couldaccordingly transmit data to the access node in those PRBs distributedacross the carriers. Further, the UE could regularly report to theaccess node the UE's coverage quality per component carrier, tofacilitate MCS selection and other operations.

Yet further, as the industry advances from one generation of wirelesstechnology to the next, or in other scenarios, networks and UEs may alsosupport dual-connectivity service, where a UE is served on multipleco-existing connections, perhaps according to different respective RATs.

For instance, a first access node could be configured to provide serviceaccording to a first RAT and a second access node could be configured toprovide service according to a second RAT, and a UE positionedconcurrently within coverage of both the first and second access nodescould have a first radio configured to engage in service according tothe first RAT and a second radio configured to engage in serviceaccording to the second RAT. The UE may thus be able to establish afirst air-interface connection with the first access node according tothe first RAT and a second air-interface connection with the secondaccess node according to the second RAT, and the access nodes may thenconcurrently serve the UE over those connections according to theirrespective RATs, each in the manner discussed above for instance.

Such dual connectivity (or “non-standalone” (NSA) connectivity) couldalso help to facilitate increased peak data-rate of communications, bymultiplexing the UE's communications across the multiple air-interfaceconnections. Further or alternatively, dual connectivity may provideother benefits compared with serving a UE on a single connection (as“standalone” (SA) connectivity) perhaps according to a single RAT.

In a representative dual-connectivity implementation, one of the accessnodes could operate as a master node (MN), responsible for coordinatingsetup, management, and teardown of dual-connectivity service for the UEand functioning as an anchor point for RRC signaling and core-networkcontrol signaling related to the dual-connected UE. And each of one ormore other access nodes could operate as a secondary node (SN) mainly toprovide additional connectivity and increased aggregate bandwidth forthe UE.

When the UE enters into coverage of such a system, the UE couldinitially scan for coverage and discover threshold strong coverage ofthe MN on a given carrier, and the UE could then responsively engage insignaling as discussed above to establish a first air-interfaceconnection with the MN on that carrier and to attach with the network.Further, the MN may configure carrier-aggregation service for the UE byadding one or more carriers to the UE's connection with the MN, thusdefining for the UE a master cell group (MCG). And if the UE supportsdual-connectivity service, the MN might then coordinate setup of dualconnectivity for the UE.

Coordinating setup of dual connectivity for the UE could involveengaging in signaling to coordinate setup for the UE of a secondair-interface connection between the UE and the SN. For instance, the MNcould engage in signaling with the SN to arrange for establishment ofthe second connection, and the MN could engage in signaling with the UEto cause the UE to access the SN and complete setup of that secondconnection. Further, the MN and/or SN could likewise configure thissecond connection to encompass multiple carriers, thus defining for theUE a secondary cell group (SCG).

In addition, coordinating setup of dual connectivity for the UE couldalso involve engaging in signaling, for each of one or more bearersestablished for the UE, to split the bearer so that the MN and SN canthen each serve a respective portion of the UE's data communications.For instance, the MN could engage in signaling to establish a bearersplit at the core-network gateway system, with one access-bearer legextending between the gateway system and the MN and anotheraccess-bearer leg extending between the gateway system and the SN.Alternatively, the MN could engaging signaling to establish a bearersplit at the MN, with the UE's access bearer remaining anchored at theMN and a branch of the access bearer extending between the MN and theSN. And still alternatively, the MN could engage in signaling toestablish a bearer split at the SN, with the UE's access bearer beingtransferred to and anchored at the SN and a branch of the access bearerextending between the SN and the MN.

With dual-connectivity so configured by way of example, the MN and SNcould then serve the UE with packet-data communications over theirrespective connections with the UE, with each access node respectivelycoordinating air-interface communication in the manner described abovefor instance.

In an example implementation, the UE's downlink user-plane data flowwould be split between the UE's two connections. For instance, when thecore-network gateway system has packet data destined to the UE, thatdata could flow over a split bearer like one of those noted above, withthe MN ultimately receiving a portion of the data and transmitting thatportion of data over the UE's first air-interface connection to the UE,and with the SN ultimately receiving another portion of the data andtransmitting that other portion of data over the UE's secondair-interface connection to the UE. Further, the distribution of theUE's downlink user-plane data flow between the UE's connections could bedone according to a downlink split ratio. And the MN and/or anothercontroller of the UE's dual-connectivity service could be responsiblefor configuring that downlink split ratio.

Likewise, the UE's uplink user-plane data flow could also be splitbetween the UE's two connections. For instance, when the UE has data totransmit on the transport network, the UE could transmit a portion ofthat data over its first air-interface connection to the MN, and thatdata could flow over an access bearer from the MN ultimately to thecore-network gateway system for output onto the transport network, andthe UE could transmit another portion of the data over its secondair-interface connection to the SN, and that data could similarly flowover an access bearer from the SN ultimately to the core-network gatewaysystem for output onto the transport network. And analogously here, thedistribution of the UE's uplink user-plane data flow between the UE'sconnections could be done according to an uplink split ratio, and the MNand/or another controller of the UE's dual-connectivity service couldlikewise be responsible for configuring that uplink split ratio.

In addition, as to the uplink data split in an example dual-connectivityimplementation, one of the UE's connections could be designated as theUE's “primary uplink path,” and the other (or another) of the UE'sconnections could be designated as the UE's “secondary uplink path.”Further, to help conserve the UE's transmission power and battery power,the UE could be configured by default to operate in asingle-connection-uplink mode in which the UE limits its uplinkuser-plane data flow to just its primary uplink path. And uponoccurrence of a trigger, such as threshold high rate of uplink data flowfrom the UE, the UE could transition from the single-connection-uplinkmode to a split-uplink mode in which the UE will split its uplink dataflow between its primary and secondary uplink paths, applying an uplinksplit ratio as noted above, perhaps with a majority of the uplink dataflow being provided on the UE's primary uplink path.

Setting one of the UE's connections to be the UE's primary uplink pathin this arrangement could also be considered to involve setting adefault uplink split ratio for the UE, according to which the UE maytransmit 100% of its uplink user-plane data over that connection, andthe UE may transmit 0% of its uplink user-plane data over the otherconnection. Further, as with the downlink and uplink split ratios, theMN and/or another controller of the UE's dual-connectivity service couldbe responsible for controlling which of the UE's connections will be setas the UE's primary uplink path.

One technical issue in such a system, as to the downlink and/or uplink,is what split ratio should be configured for the dual-connected UE.Further, a related or subsidiary technical issue, for uplinkcommunication from the dual-connected UE is which of the UE'sconnections should be set as the UE's primary uplink path, i.e., theconnection to which the UE would restrict its uplink user-plane dataflow until a trigger condition causes the UE to transition to operate inthe split-uplink mode.

The present disclosure provides various technical mechanisms fordynamically controlling at least these aspects of dual-connectivityservice. The disclosed dynamic control could be carried out by acomputing system, which could be provided at least in part at the MN,such as by a host processor or other programmed processing unit of theMN, among other possibilities.

In particular, the disclosure provides for carrying out this dynamiccontrol based at least on one or more of the following comparisons ofmetrics per connection: (i) a comparison of spectral efficiency of thecells on which the UE is connected respectively with the MN and with theSN, (ii) a comparison of fading in the cells on which the UE isconnected respectively with the MN and with the SN, (iii) a comparisonof insertion loss as to the cells on which the UE is connectedrespectively with the MN and with the SN, (iv) a comparison ofbeamforming support respectively on the UE's connections with the MN andwith the SN, (v) a comparison of MIMO support respectively on the UE'sconnections with the MN and with the SN, and (vi) a comparison ofaggregate frequency bandwidth of the UE's connections respectively withthe MN and with the SN, among other possibilities.

Based at least on one or more such comparisons, for instance, thecomputing system could determine and set a split ratio for the UE. Forinstance, as to a given such metric that is a desirable servicecharacteristic, such as spectral efficiency, beamforming support, MIMOsupport, or aggregate bandwidth, the MN might set a split ratio thatputs a majority of the UE's data flow on the air-interface connectionthat has the highest level of the metric. Whereas, as to a given suchmetric that is an undesirable service characteristic, such as insertionloss or fading, the computing system might set a split ratio that puts amajority of the UE's data flow on the air-interface connection that hasthe lowest level of the metric. Further, the computing system couldcompute respectively per connection a weighted score of multiple suchmetrics and could then set a split ratio for the UE based on acomparison of the connections' weighted scores.

In addition or as part of this process, based on one or more suchcomparisons, the computing system could also select and set one of theUE's connections to be the UE's primary uplink path. For instance, thecomputing system might set as the UE's primary uplink path theconnection that has the highest level of one or more desirable metricsand/or the lowest level of one or more undesirable metrics, and/orlikewise based on a comparison of the connections' weighted scores.

These as well as other aspects, advantages, and alternatives will becomeapparent to those of ordinary skill in the art by reading the followingdetailed description, with reference where appropriate to theaccompanying drawings. Further, it should be understood that thedescriptions provided in this overview and below are intended toillustrate the invention by way of example only and not by way oflimitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an example wirelesscommunication system in which features of the present disclosure can beimplemented.

FIG. 2 is a flow chart depicting operations that can be carried out inaccordance with the disclosure.

FIG. 3 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 4 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 5 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 6 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 7 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 8 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 9 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 10 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 11 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 12 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 13 is another flow chart depicting operations that can be carriedout in accordance with the disclosure.

FIG. 14 is a simplified block diagram of an example computing systemoperable in accordance with the disclosure.

FIG. 15 is a simplified block diagram of an example access node operablein accordance with the disclosure.

DETAILED DESCRIPTION

An example implementation will now be described in the context of 4GLTE, 5G NR, and 4G-5G dual connectivity, referred to as EUTRA-NR DualConnectivity (EN-DC).

With EN-DC, a 4G access node (4G evolved Node-B (eNB)) functions as theMN, and a 5G access node (5G next-generation Node-B (gNB)) functions theSN. Thus, a UE would first establish a standalone-4G connection with a4G eNB, and the 4G eNB could then coordinate setup of EN-DC service forthe UE, including setup for the UE of a secondary 5G connection with the5G gNB. And the 4G eNB and 5G gNB could then concurrently serve the UEover their respective 4G and 5G connections with the UE.

It should be understood, however, that the principles disclosed hereincould extend to apply with respect to other scenarios as well, such aswith respect to other RATs and other dual-connectivity configurations,including possibly single-RAT dual connectivity and/or dual-connectivityencompassing more than two connections. Further, it should be understoodthat other variations from the specific arrangements and processesdescribed are possible. For instance, various described entities,connections, functions, and other elements could be added, omitted,distributed, re-located, re-ordered, combined, or changed in other ways.In addition, it will be understood that technical operations disclosedas being carried out by one or more entities could be carried out atleast in part by a processing unit programmed to carry out theoperations or to cause one or more other entities to carry out theoperations

Referring to the drawings, FIG. 1 is a simplified block diagram of anexample network arrangement having a 4G eNB 12 and a 5G gNB 14. Each ofthese access nodes could be macro access nodes of the type configured toprovide a wide range of coverage or could take other forms, such as asmall cell access node, a relay, a femtocell access node, or the like,possibly configured to provide a smaller range of coverage. Further, theaccess nodes could be collocated with each other, e.g., at a common cellsite with collocated RF points of origin, or could be separatelylocated. Either way, the access nodes could be optimally configured toprovide overlapping coverage in order to support EN-DC service.

Each of these access nodes could also be configured to provide coverageand service on one or more carriers, with the access node's coverage ona given carrier defining a respective cell as noted above. In theexample shown, for instance, the 4G eNB 12 is configured to providecoverage and service on one or more 4G carriers 16, and the 5G gNB 14 isconfigured to provide coverage and service on one or more 5G carriers18.

Each such carrier could be defined in a given frequency band and couldbe FDD or TDD. And each carrier could have a respective frequencybandwidth on its downlink and/or uplink. For instance, an FDD carriercould have a respective downlink frequency bandwidth and a respectiveuplink frequency bandwidth. Whereas, a TDD carrier could have a singlechannel bandwidth for both downlink and uplink, though thedownlink-uplink configuration of the TDD carrier could alternatively beconsidered to scale down the bandwidth of the carrier respectively onthe downlink and uplink based on what percentage of time the carrier isdownlink versus uplink.

To facilitate providing service and coverage on the illustratedcarriers, the access nodes could each have a respective antennastructure, such as an antenna array, that is configured to transmit andreceive electromagnetic signals in a region defined by an antennapattern or radiation pattern, or the access nodes could share portionsof a common antenna array for this purpose, among other possibilities.

Further, for each such carrier on which an access node operates, orgenerally, the access node might have a respective set of RF equipment,such as respective antenna elements, and respective antenna ports,jumper cables, filters, amplifiers, and various other componentspossibly including and/or extending between a radio and the antennaelements, that the access node would use for air-interface communicationon the carrier. As shown in FIG. 1 , for instance, the 4G eNB 12 mayhave one or more sets of RF equipment 20 for serving air-interfacecommunications on 4G carrier(s) 16, and the 5G gNB 14 may have one ormore sets of RF equipment 22 for serving air-interface communications on5G carrier(s) 18.

The air interface on each such carrier could be structured as describedabove by way of example, being divided over time into frames, subframes,and symbol time segments, and over frequency into subcarriers, thusdefining an array of air-interface resource elements grouped into PRBsallocable by the access node as noted above, for use to carry data to orfrom served UEs. Carrier-structure and/or service on the 4G and 5Gair-interfaces, however, could differ from each other in various waysnow known or later developed, such as with one implementing variablesubcarrier spacing and the other having fixed subcarrier spacing, withone having flexible TDD configuration and the other having fixed TDDconfiguration, with one having different subcarrier spacing and/orsymbol time segment length than the other, and/or with one makingdifferent use of MIMO technologies than the other, among otherpossibilities.

As further shown in FIG. 1 , the example arrangement includes twoexample core networks, designated as a 4G core network 24 and a 5G corenetwork 26, each providing connectivity with an external transportnetwork 38 such as the Internet for instance.

Each of these core networks could be a packet-switched network thatsupports virtual-packet tunnels or other interfaces between networknodes. And each network could include both a user-plane subsystemthrough which UE bearer communications could flow to and from thetransport network 38, and a control-plane subsystem supporting functionssuch as UE authentication, mobility management, and bearer management,among others. The 4G and 5G core networks, however, may differ from eachin various ways, such as with the 5G core network providing advancedslicing or other service options.

In the example arrangement shown, both the 4G eNB 12 and 5G gNB 14 areinterfaced with the 4G core network 24, but of those two access nodes,just the 5G gNB 14 is interfaced with the 5G core network 26. Inpractice, the 4G core network 24 could be the core network for UEsserved with standalone 4G connectivity by the 4G eNB 12 and for UEsserved with EN-DC by the 4G eNB 12 and the 5G gNB 14. Whereas, the 5Gcore network 26 could be the core network for UEs served with standalone5G connectivity by the 5G gNB 14. For simplicity, representativeelements of the 4G core network 24 are shown, but details of the 5G corenetwork 26 are not shown.

As shown, for instance, the core network 24 could be an Evolved PacketCore (EPC) network and could include a serving gateway (SGW) 28, apacket data network gateway (PGW) 30, a mobility management entity (MME)32, a home subscriber server (HSS) 34, and an element management system(EMS) 36, although other arrangements are possible as well.

In an example implementation, without limitation, the 4G eNB 12 and 5GgNB 14 could each have an interface with the SGW 28, the SGW 28 couldhave an interface with the PGW 30, and the PGW 30 could provideconnectivity with the transport network 38 such as the Internet.Further, the 4G eNB 12 could have interfaces with the 5G gNB 14 and withthe MME 32, and the MME 32 could have an interface with the SGW 28, sothat the MME 32 could coordinate setup of bearers for UEs to enable theUEs to engage in packet-data communications on the transport network 38.

Still further, the HSS 34 could store or have access to UE profilerecords, which could specify service-subscription plans, UEconfigurations, and/or other such UE capability information, such aswhether a UE is EN-DC capable for instance. And the EMS 36 could operateas a central repository of operational data for the wirelesscommunication network and to control and manage operation of variousnetwork elements such as the access nodes.

FIG. 1 also depicts various example UEs 40 that may from time to time bewithin coverage of the illustrated access nodes. Each of these UEs couldtake any of the forms noted above, among other possibilities. Further,some or all these UEs could be equipped with a 4G LTE radio and/or a 5GNR radio, and could have associated circuitry and logic to support 4GLTE service and/or 5G NR service, and perhaps EN-DC service. Further,the 4G eNB 12 and 5G gNB 14 could be configured to serve multiple suchUEs at once.

Upon entering into coverage this example system, a representative suchUE could scan for and discover coverage of a given access node and couldthen responsively engage in signaling to connect with the access node asdiscussed above.

For instance, if the UE supports just 4G service or if the UE supportsEN-DC service, the UE might initially scan for 4G coverage and discoverthreshold strong coverage of 4G eNB 12 on a 4G carrier 16, and the UEmay then responsively engage in random access and RRC signaling with the4G eNB 12 to establish a 4G connection between the UE and the 4G eNB 12on that carrier. Further, the 4G eNB 12 may add one or more other 4Gcarriers 16 to the UE's 4G connection to provide the UE with 4Gcarrier-aggregation service.

Whereas, if the UE supports just 5G service, the UE might initially scanfor 5G coverage and discover threshold strong coverage of the 5G gNB 14on a 5G carrier 18, and the UE may then responsively engage in randomaccess and RRC signaling with the 5G gNB 14 to establish a 5G connectionbetween the UE and the 5G gNB 14 on that carrier. And the 5G gNB 14could likewise add one or more other 5G carriers 18 to the UE's 5Gconnection to provide the UE with 5G carrier-aggregation service.

Once the UE is connected with an access node, the UE may then furthertransmit to the access node an attach request message, which the accessnode may forward to a core-network controller to trigger setup for theUE of one or more user-plane bearers as noted above. Further, the accessnode could establish in data storage a context record for the UE asnoted above, and the access node could then serve the UE withpacket-data communications over the UE's connection as discussed above.

For example, once a UE connects with the 4G eNB 12, the UE could send anattach request message, which the 4G eNB 12 could forward to MME 32 forprocessing. Upon authenticating and authorizing the UE for service, theMME 32 and 4G eNB 12 could then coordinate setup for the UE of at leastone user-plane bearer. For instance, the MME 32 could engage insignaling with the 4G eNB 12 and the SGW 28 to coordinate setup for theUE of an S1-U packet tunnel between the 4G eNB 12 and the SGW 28, andthe SGW 28 could responsively engage in signaling with the PGW 30 tocoordinate setup for the UE of an associated S5 packet tunnel betweenthe SGW 28 and the PGW 30. Further, the 4G eNB 12 could engage insignaling with the UE to establish for the UE an associated data radiobearer. And once the UE is so connected and attached, the 4G eNB 12could then serve the UE in a standalone 4G mode, in the manner discussedabove.

In addition, when a UE connects with an access node, and/or at othertimes, the access node may obtain capability data that indicates variouscapabilities of the UE, such as whether the UE is dual-connectivity(e.g., EN-DC) capable, and whether and to what extent the UE supportsMIMO and other service features. For instance, the access node couldobtain this capability data from the UE and/or from the core-networkcontroller and HSS 34. And the access node could store the capabilitydata in the UE context record for reference while serving the UE.

For each such EN-DC capable UE that connects with the 4G eNB 12, the 4GeNB 12, operating as MN, could then work to configure EN-DC service forthe UE.

For instance, the 4G eNB 12 could first determine that the UE is withinthreshold strong coverage of the 5G gNB 14 on one or more 5G carriers18, perhaps based on measurement reporting from the UE or based oncoverage assumptions. And the 4G eNB 12 could then engage in signalingto configure for the UE a secondary 5G connection with the 5G gNB 14 onthe one or more 5G carriers. For example, the 4G eNB 12 could transmitto the 5G gNB 14 an SN-Addition request to cause the 5G gNB 14 toallocate resources for a 5G connection for the UE on the one or more 5Gcarriers 18, the 4G eNB 12 could receive an SN-Addition-Requestacknowledge message from the 5G gNB 14, and the 4G eNB 12 could engagein associated RRC signaling with the UE, in response to which the UEcould then access and complete establishment of the 5G connection.Further, the 4G eNB 12 could engage in signaling to establish a splitbearer, such to transfer the UE's access bearer (e.g., the UE's S1-Utunnel) to the 5G gNB 14 and to arrange for a bearer split at the 5G gNB14.

With EN-DC service configured for the UE, the 4G eNB 12 and 5G gNB 14could then concurrently serve the UE, each over its respectiveconnection with the UE and each in the manner discussed above—such aslearning of the UE's channel quality to establish an applicable MCS,scheduling PRB allocation for air-interface communication with the UE,and so forth.

Further, the UE's data flow could be split between the UE's 4G and 5Gconnections as discussed above. For instance, when the PGW 30 receivesuser-plane data from the transport network 38 for transmission to theUE, that data may flow over a split access bearer, and the 4G eNB 12 maytransmit a portion of the data over the UE's 4G connection to the UE,while the 5G gNB 14 may transmit another portion of the data over theUE's 5G connection to the UE. And when the UE has user-plane data totransmit on the transport network 38, the UE may transmit a portion ofthe data over its 4G connection to the 4G eNB 12, which may forward thedata over an access bearer for transmission directly or indirectlythrough the core network 24 to the transport network 38, and the UE maytransmit another portion of the data over its 5G connection to the 5GgNB 14, which may likewise forward the data over an access bearer fortransmission directly or indirectly through the core network 24 to thetransport network 38.

And the UE may treat one of the UE's connections as the UE's primarypath as discussed above, restricting the UE's uplink data flow to thatconnection until the level of data flow rises to a threshold level orother reason exists to offload some of the data flow to the UE's otherconnection.

In line with the discussion above, a computing system could determinewhat split ratio should be used for the UE's data flow, perhapsrespectively for the downlink and for the uplink, and the computingsystem could cause the determined data split to be applied. Further, thecomputing system could decide which of the UE's connections will be theUE's primary path, and the computing system could cause the UE tooperate accordingly. In practice, the computing system could be providedat the 4G eNB 12, at the 5G eNB 14, and/or elsewhere, possibly even atthe UE.

Controlling the UE's downlink split ratio could involve setting thedownlink split ratio at the point where the downlink split would occur,such as signaling to, programming, and/or otherwise provisioning theentity that will perform the downlink data split, so as to cause thatentity to programmatically apply the desired downlink split ratio. Forinstance, if the downlink split will occur at the SGW 28, this couldinvolve setting the SGW 28 apply the downlink split ratio. Whereas, ifthe downlink split will occur at the 4G eNB 12, this could involvesetting the 4G eNB 12 to apply the downlink split ratio. And if thedownlink split will occur at the 5G gNB, this could involve setting the5G gNB 14 to apply the downlink split ratio.

Controlling the UE's uplink split ratio, on the other hand, couldinvolve engaging in RRC signaling or the like with the UE to direct andthus cause the UE to apply the desired uplink split ratio. For instance,this could involve the 4G eNB 12, as the UE's MN, transmitting to the UEan RRC connection reconfiguration message that specifies what uplinksplit ratio the UE should apply, and the UE responsively setting itselfto apply that uplink split ratio.

Further, controlling the UE's primary uplink path could likewise involveengaging in RRC signaling or the like with the UE to direct and thuscause the UE to treat a designated connection as the UE's primary uplinkpath. For instance, this could involve the 4G eNB 12, as the UE's MN,transmitting to the UE an RRC connection reconfiguration message thatspecifies which of the UE's connections the UE treat as the UE's primaryuplink path, and the UE responsively setting itself to operateaccordingly.

In addition, the computing system that carries out these controloperations could dynamically repeat the process and vary the settingsover time as conditions and considerations change. For instance, afterhaving set the UE's downlink split ratio to a first determined downlinksplit ratio, the computing system could later set the UE's downlinksplit ratio to a second, different determined downlink split ratio.Likewise, after having set the UE's uplink split ratio to a firstdetermined uplink split ratio, the computing system could later set theUE's uplink split ratio to a second, different determined uplink splitratio. And after having set one of the UE's to be the UE's primaryuplink path, the computing system could later set the UE's otherconnection to be the UE's primary uplink path.

In an example implementation, the 4G eNB 12, as the UE's MN, could beresponsible for carrying out these control operations.

For instance, the 4G eNB 12 could determine what downlink split ratio toapply for the UE, and the 4G eNB 12 could then cause that determineddownlink split ratio to be applied. For example, if the UE's downlinksplit occurs at the 4G eNB 12, then the 4G eNB 12 could set itself toapply the determined downlink split ratio, according to which the 4G eNB12 would transmit to the UE over the UE's 4G connection a portion of theUE's downlink user-plane data flow and would forward to the 5G gNB 14for transmission to the UE over the UE's 5G connection another portionof the UE's downlink user-plane data flow. Whereas, if the UE's downlinkdata split occurs at the 5G gNB 14, then the 4G eNB 12 could transmit tothe 5G gNB 14 a directive to which the 5G gNB 14 could respond bysetting itself to apply the determined downlink split ratio. Analogousprocessing could also occur if the downlink split is elsewhere, such asat the SGW 28.

Likewise, the 4G eNB 12 could determine what uplink split ratio to applyfor the UE (perhaps the same as the downlink split ratio, or perhapsdifferent) and could cause the UE to apply the determined uplink splitratio. For example, the 4G eNB 12 could transmit to the UE an RRCconnection reconfiguration message specifying the determined uplinksplit ratio, to which the UE could respond by implementing the uplinksplit ratio, accordingly transmitting a portion of the UE's uplinkuser-plane data flow over the UE's 4G connection to the 4G eNB 12 andtransmitting another portion of the UE's uplink user-plane data flowover the UE's 5G connection to the 5G gNB 14.

Further or as part of establishing the UE's uplink split ratio, the 4GeNB 12 could determine which of the UE's connections should be the UE'sprimary uplink path. And the 4G eNB 12 could transmit to the UE an RRCconnection reconfiguration message that directs the UE to treat thedetermined connection as the UE's primary uplink path, to which the UEcould respond accordingly.

Alternatively, the 5G gNB 14 could carry out some or all of thesecontrol functions. For instance, the 5G gNB 14 could analogouslydetermine what downlink split ratio should be applied for the UE andcould analogously cause that downlink split ratio to be applied. And/orthe 5G gNB 14 could analogously determine what uplink split ratio shouldbe applied for the UE and/or what connection should be the UE's primaryuplink path and could analogously cause that uplink split ratio orprimary uplink path setting to be applied, possibly signaling to the 4GeNB 12 to cause the 4G eNB 12 to engage in RRC signaling with the UE tocause the UE to operate accordingly.

In addition, as noted above, the computing system could take intoaccount one or more per-connection metrics as a basis to carry out thesedynamic control operations. For instance, as to a given metric that isdesirable, the computing system could establish for the UE a split ratiothat puts a majority of the UE's data flow on the connection having ahigher value of that metric, or as to a given metric that isundesirable, the computing system could established for the UE splitratio that puts a majority of the UE's data flow on the connectionhaving a lower value of that metric. And the computing system couldconsider multiple metrics in combination, such as by establishing perconnection a weighted score based on multiple metrics, and thenestablishing the data split based on a comparison of the connections'respective weighted scores.

Further, the establishing of the split ratio or decision of whichconnection should be the UE's primary uplink path could be done in realtime while the UE is dual connected or could be done before the UE isdual connected, to facilitate controlling the UE's split ratio and/orprimary uplink path when the UE is dual connected.

The following sub-sections will now discuss various such metrics asfactors that the computing system could use, alone or in combinationwith each other and/or with other factors, as a basis to dynamicallycontrol the split ratio that will be used for a dual-connected UE's dataflow, and perhaps further or as part of that process, to control whichof the UE's connections the UE will use as the UE's primary uplink path.For simplicity, these sub-sections will address example implementationby the 4G eNB 12. But it should be understood that other implementationsare possible as well.

Controlling the UE's Data Split Based on Per-Connection SpectralEfficiency

One basis that the 4G eNB 12 could use for this dynamic control is acomparison of spectral efficiency of the cells on which the UE isconnected respectively with the 4G eNB 12 and with the 5G gNB 14.

Spectral efficiency of a cell is a measure of the data rate that thecell supports per unit of frequency spectrum, typically represented as aquantity of bits per second per Hertz (i.e., bits/s/Hz), and typicallywith respect to the underlying baseband data being communicated,excluding overhead such as error-correction bits. In general, if the UEsserved by a cell tend to have relatively good channel quality and/or ifthe cell otherwise tends to serve the UEs with relatively high datarates per unit of frequency spectrum, then the cell would haverelatively high spectral efficiency, which would represent a relativelydesirable context for serving any given UE. Whereas, if the UEs servedby a cell tend to have relatively poor channel quality and/or if thecell otherwise tends serves UEs with relatively low data rates per unitof frequency spectrum, then the cell would have relatively low spectralefficiency, which would represent a less desirable (or a relativelyundesirable) context for serving any given UE.

Accordingly, the 4G eNB 12 could determine spectral efficiency of theUE's 4G connection as or otherwise based on spectral efficiency of theone or more 4G cells on which the UE is connected with the 4G eNB 12,and the 4G eNB 12 could determine spectral efficiency of the UE's 5Gconnection as or otherwise based on spectral efficiency of the one ormore 5G cells on which the UE is connected with the 5G gNB 14. The 4GeNB 12 could then compare the determined spectral efficiency of the UE's4G connection with the determined spectral efficiency of the UE's 5Gconnection. And based at least on that comparison, the 4G eNB 12 coulddetermine and set a split ratio for the UE.

For instance, based at least on this comparison, the 4G eNB 12 could seta split ratio that puts a majority of the UE's data flow on the UE'sconnection that has the highest determined spectral efficiency, perhapssetting the split ratio to be equal to or otherwise based on a ratio ofthe connections' respective determined spectral efficiencies. Forexample, if the determined spectral efficiency of the UE's 5G connectionis twice that of the UE's 4G connection, then the 4G eNB 12 could set asplit ratio that puts twice as much of the UE's data flow on the UE's 5Gconnection as on the UE's 4G connection. Further, the 4G eNB 12 couldcarry out this process separately for the UE's downlink data flow basedon a comparison of determined spectral efficiencies of the downlinks ofthe UE's connections, and for the UE's uplink data flow based on acomparison of determined spectral efficiencies of the uplinks of theUE's connections.

In addition or as part of this process, based at least on thespectral-efficiency comparison, the 4G eNB 12 could also select and setone of the UE's connections as the UE's primary uplink path, such as byselecting and setting as the UE's primary uplink path the connectionthat has the highest determined spectral efficiency.

To facilitate this process, the 4G eNB 12 could determine respectivespectral efficiencies of the UE's 4G connection and 5G connection, basedon records of the spectral efficiency and/or records that establish thespectral efficiency. In practice, for instance, the 4G eNB 12 and 5G gNB14 could each keep records tracking spectral efficiency respectively ofeach of the one or more cells on which they operate, and the 5G gNB 14could report such records to the 4G eNB 12. Alternatively oradditionally, the EMS 36 could track such per-cell spectral efficiencyand could report the spectral efficiency to the 4G eNB 12, among otherpossibilities.

On a per-cell basis, for instance, these records could establishspectral efficiency as a measure of total bit rate served in the celldivided by frequency bandwidth of the cell. Further, the spectralefficiency of a given cell could be a measure of spectral efficiency forthe cell generally (e.g., across all service in the cell) and could thusencompass both NSA and SA service in the cell and service as to one ormore UEs other than the UE at issue. Measures of spectral efficiency ofa given cell could also be rolled up over a sliding window of time, toestablish a most recent representative spectral efficiency measureand/or could establish a representative measure of spectral efficiencyfor at a particular time of day based on historical performance at thattime of day, any of which could be a basis for the analysis.

As noted above, at issue could be a comparison of (i) spectralefficiency of the 4G cell(s) on which the UE is connected with the 4GeNB 12 with (ii) spectral efficiency of the 5G cell(s) on which the UEis connected with the 5G gNB 14, possibly limiting the downlink oruplink focus to just those cells that would be used in practice for theUE's downlink or uplink service respectively. For instance, respectivelyfor each of the UE's connections, the 4G eNB 12 could determine whichcell(s) the UE is connected and operating on, and the 4G eNB 12 coulddetermine an average or other rolled up measure of spectral efficiencyof the determined cell(s). The 4G eNB 12 could then compare thosedetermined levels of spectral efficiency of the UE's connections as abasis to set the UE's data split ratio and/or primary uplink path.

Further, as noted above, the 4G eNB 12 could consider additional factorsin this process as well.

FIG. 2 is a flow chart depicting an example method that could be carriedout in accordance with the present disclosure to control data split of aUE when the UE has at least two co-existing air-interface connectionsincluding a first air-interface connection with a first access node anda second air-interface connection with a second access node. Asdiscussed above, this method could be carried out by a computing system,such as by at least one of the two access nodes for instance.

As shown in FIG. 2 , at block 42, the example method includes comparinga level of spectral efficiency of the first air-interface connectionwith a level of spectral efficiency of the second air-interfaceconnection. At block 44, the method then includes, based at least on thecomparing, establishing a split ratio defining a distribution of dataflow of the UE between at least the first air-interface connection andthe second air-interface connection. And at block 46, the methodincludes, based on the establishing, causing the established split ratioto be applied.

In line with the discussion above, the split ratio at issue in thismethod could be an uplink split ratio and/or a downlink split ratio.Further, if the split ratio is an uplink split ratio, the act of causingthe established split ratio to be applied could involve transmitting tothe UE a directive that causes the UE to apply the established splitratio. And if the split ratio is a downlink split ratio, in a scenariowhere an entity splits the downlink data flow of the UE between thefirst and second connections, the act of causing the established splitratio to be applied could involve causing the entity to apply theestablished downlink split ratio.

As further discussed above, the method could additionally include (i)determining the level of spectral efficiency of the first air-interfaceconnection based on spectral efficiency of one or more cells on whichthe first air-interface connection is defined and (ii) determining thelevel of spectral efficiency of the second air-interface connectionbased on spectral efficiency of one or more cells on which the secondair-interface connection is defined. And the act of comparing the levelof spectral efficiency of the first air-interface connection with thelevel of spectral efficiency of the second air-interface connectioncould involve comparing the determined level of spectral efficiency ofthe first air-interface connection with the determined level of spectralefficiency of the second air-interface connection.

Further, the act of establishing the split ratio based on the comparingof the determined level of spectral efficiency of the firstair-interface connection with the determined level of spectralefficiency of the second air-interface connection could involveestablishing the split ratio based on a ratio of (i) the determinedlevel of spectral efficiency of the first air-interface connection to(ii) the determined level of spectral efficiency of the secondair-interface connection. For instance, this could involve setting thesplit ratio to be equal to the ratio of (i) the determined level ofspectral efficiency of the first air-interface connection to (ii) thedetermined level of spectral efficiency of the second air-interfaceconnection.

Still further, the act of establishing the split ratio based on thecomparing of the determined level of spectral efficiency of the firstair-interface connection with the determined level of spectralefficiency of the second air-interface connection could involve (i)selecting one of the first and second air-interface connections based onthe determined level of spectral efficiency of the selectedair-interface connection being higher than the determined level ofspectral efficiency of the other of the first and second air-interfaceconnections and (ii) based on the selecting, establishing as the splitratio a split ratio that will put a majority of the data flow of the UEon the identified air-interface connection.

FIG. 3 is next a flow chart depicting an example method that could becarried out in accordance with the present disclosure to control uplinkcommunication from a UE when the UE has at least two co-existingair-interface connections including a first air-interface connectionwith a first access node and a second air-interface connection with asecond access node, where one of the first and second air-interfaceconnections defines a primary uplink path of the UE to which the UErestricts uplink user-plane transmission from the UE unless and until atrigger condition causes the UE to split the uplink user-planetransmission between the first and second air-interface connections.

As shown in FIG. 3 , at block 48, the method includes comparing a levelof spectral efficiency of the first air-interface connection with alevel of spectral efficiency of the second air-interface connection. Atblock 50, the method then includes selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE. And at block 52, the method includescausing the UE to operate in accordance with the selecting.

In line with the discussion above, this method could be carried out by agiven one of the access nodes. And the act of causing the UE to operatein accordance with the selecting could involve transmitting from thegiven access node to the UE a directive that causes the UE to use theselected air-interface connection as the primary uplink path of the UE.

Further, as discussed above, the act of selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE could involve (i) determining, basedon the comparing, that the level of spectral efficiency of the firstair-interface connection is greater than the level of spectralefficiency of the second access node and (ii) based at least on thedetermining, selecting the first air-interface connection to be theprimary uplink path of the UE.

In addition, as discussed above, the method as so defined could alsoinvolve (i) determining the level of spectral efficiency of the firstair-interface connection based on spectral efficiency of one or morecells on which the first air-interface connection is defined and (ii)determining the level of spectral efficiency of the second air-interfaceconnection based on spectral efficiency of one or more cells on whichthe second air-interface connection is defined. And in that case, theact of comparing the level of spectral efficiency of the firstair-interface connection with the level of spectral efficiency of thesecond air-interface connection could likewise involve comparing thedetermined level of spectral efficiency of the first air-interfaceconnection with the determined level of spectral efficiency of thesecond air-interface connection.

Various other features discussed herein can be implemented in thiscontext as well, and vice versa.

Controlling the UE's Data Split Based on Per-Connection Fading

Another basis that the 4G eNB 12 could use for this dynamic control is acomparison of fading in the cells on which the UE is connectedrespectively with the 4G eNB 12 and with the 5G gNB 14.

Fading in a cell could be a measure of an extent to which UEs served inthe cell tend to experience fluctuation in coverage quality of the cellover time, and particularly an extent to which the UEs tend toexperience a degradation in such coverage quality over time. Fadingcould occur for various reasons, such as because UEs move farther awayfrom the access node serving the cell and/or because of multipathinterference or shadowing issues at various locations in the cell, amongother possibilities. If UEs in a cell tend to experience a relativelyhigh level of fading, that could represent a relatively undesirablecontext for serving any given UE in the cell, as the likelihood offading could suggest a likelihood of degraded or unstable communicationquality. Whereas if UEs in a cell tend to experience a relatively lowlevel of fading, that could represent a relatively desirable context forserving any given UE in the cell.

Accordingly, the 4G eNB 12 could determine a level of fading associatedwith the UE's 4G connection as or otherwise based on fading experiencedin the one or more 4G cells on which the UE is connected with the 4G eNB12, and the 4G eNB 12 could determine a level of fading associated withthe UE's 5G connection as or otherwise based on fading experienced inthe one or more 5G cells on which the UE is connected with the 5G gNB14. The 4G eNB 12 could then compare the determined level of fadingassociated with the UE's 4G connection with the determined level offading associated with the UE's 5G connection. And based at least onthat comparison, the 4G eNB 12 could determine and set a split ratio forthe UE.

For instance, based at least on this comparison, the 4G eNB 12 could seta split ratio that puts a majority of the UE's data flow on the UE'sconnection that has the lowest determined level of fading, perhapssetting the split ratio to be equal to or otherwise based on an inverseof a ratio of the connections' respective determined levels of fading.For example, if the determined level of fading of the UE's 5G connectionis twice that of the UE's 4G connection, then the 4G eNB 12 could set asplit ratio that puts half as much of the UE's data flow on the UE's 5Gconnection as on the UE's 4G connection. Further, the 4G eNB 12 couldcarry out this process separately for the UE's downlink data flow basedon a comparison of determined levels of fading of the downlinks of theUE's connections, and for the UE's uplink data flow based on acomparison of determined levels of fading of the uplinks of the UE'sconnections.

In addition or as part of this process, based at least on the fadingcomparison, the 4G eNB 12 could also select and set one of the UE'sconnections as the UE's primary uplink path, such as by selecting andsetting as the UE's primary uplink path the connection that has thelowest determined level of fading.

To facilitate this process, the 4G eNB 12 could determine respectivelevels of fading of the UE's 4G connection and 5G connection, based onrecords of the levels of fading and/or records that establish the levelsof fading. In practice, for instance, the 4G eNB 12 and 5G gNB 14 couldeach keep records tracking level of fading respectively in each of theone or more cells on which they operate, and the 5G gNB 14 could reportsuch records to the 4G eNB 12. Alternatively or additionally, the EMS 36could track such per-cell fading and could report the fading to the 4GeNB 12, among other possibilities.

On a per-cell basis, for instance, these records could establish fadingas a statistically rolled up measure of fading experienced by UEs servedin the cell. Further, the level of fading per cell could be a level offading for the cell generally (e.g., across all service in the cell) andcould thus encompass both NSA and SA service in the cell and service asto one or more UEs other than the UE at issue.

For instance, for each UE served in a given cell, the serving accessnode could keep timestamped records of the UE's coverage quality of thecell over time and the access node could compute a level of fadingexperienced by that UE as a rate of fluctuation of the UE's coveragequality of the cell over time—such as with a higher level of fadingcorresponding with greater rate and/or magnitude of change in coveragequality over time and a lower level of fading corresponding with lesserrate and/or magnitude of change in such coverage quality over time. Andover a sliding window of time, the serving access node or othercomputing system could roll up the latest such levels of fading formultiple UEs served in the cell, to establish a latest representativemeasure of fading of the cell.

For instance, this could involve maintaining a running average of themost recently determined level of fading of UEs served in the cell, as alatest level of fading of the cell. Alternatively or additionally, thiscould involve establishing an historical such level of fading of thecell per time of day, to facilitate predicting what the level of fadingof the cell is likely to be at a current time of day based on what thelevel of fading of the cell has been on past days at or around the sametime of day for instance.

Further, this level of fading could be focused specifically on instancesof coverage-quality fluctuation to or from a level of coverage qualitythat is deemed particularly poor, such as a predefined threshold lowlevel of RSRP or CQI for instance. And the level of fading could befurther focused on instances of coverage-quality fluctuation to a poorlevel of coverage quality, i.e., where coverage quality has degradedover time. The analysis could thus selectively omit other instances ofcoverage-quality variation.

As noted above, at issue could be a comparison of (i) level of fading ofthe 4G cell(s) on which the UE is connected with the 4G eNB 12 with (ii)level of fading of the 5G cell(s) on which the UE is connected with the5G gNB 14, possibly limiting the downlink or uplink focus to just thosecells that would be used in practice for the UE's downlink or uplinkservice respectively. For instance, respectively for each of the UE'sconnections, the 4G eNB 12 could determine which cell(s) the UE isconnected and operating on, and the 4G eNB 12 could determine an averageor other rolled up measure of level of fading of the determined cell(s).The 4G eNB 12 could then compare those determined levels of fading ofthe UE's connections as a basis to set the UE's data split ratio and/orprimary uplink path.

Further, as noted above, the 4G eNB 12 could consider additional factorsin this process as well.

FIG. 4 is a flow chart depicting an example method that could be carriedout in accordance with the present disclosure to control data split of aUE when the UE has at least two co-existing air-interface connectionsincluding a first air-interface connection with a first access node anda second air-interface connection with a second access node. Asdiscussed above, this method could be carried out by a computing system,such as by at least one of the two access nodes for instance.

As shown in FIG. 4 , at block 54, the example method includes comparinga level of fading of the first air-interface connection with a level offading of the second air-interface connection. At block 56, the methodthen includes, based at least on the comparing, establishing a splitratio defining a distribution of data flow of the UE between at leastthe first air-interface connection and the second air-interfaceconnection. And at block 58, the method includes, based on theestablishing, causing the established split ratio to be applied.

In line with the discussion above, the split ratio at issue in thismethod could be an uplink split ratio and/or a downlink split ratio.Further, if the split ratio is an uplink split ratio, the act of causingthe established split ratio to be applied could involve transmitting tothe UE a directive that causes the UE to apply the established splitratio. And if the split ratio is a downlink split ratio, in a scenariowhere an entity splits the downlink data flow of the UE between thefirst and second connections, the act of causing the established splitratio to be applied could involve causing the entity to apply theestablished downlink split ratio.

As further discussed above, the method could additionally include (i)determining the level of fading of the first air-interface connectionbased on fading experienced in one or more cells on which the firstair-interface connection is defined and (ii) determining the level offading of the second air-interface connection based on fadingexperienced in one or more cells on which the second air-interfaceconnection is defined. And the act of comparing the level of fading ofthe first air-interface connection with the level of fading of thesecond air-interface connection could involve comparing the determinedlevel of fading of the first air-interface connection with thedetermined level of fading of the second air-interface connection.

Further, the act of establishing the split ratio based on the comparingof the determined level of fading of the first air-interface connectionwith the determined level of fading of the second air-interfaceconnection could involve establishing the split ratio based on aninverse of a ratio of (i) the determined level of fading of the firstair-interface connection to (ii) the determined level of fading of thesecond air-interface connection. For instance, this could involvesetting the split ratio to be equal to the inverse of the ratio of (i)the determined level of fading of the first air-interface connection to(ii) the determined level of fading of the second air-interfaceconnection.

Still further, the act of establishing the split ratio based on thecomparing of the determined level of fading of the first air-interfaceconnection with the determined level of fading of the secondair-interface connection could involve (i) selecting one of the firstand second air-interface connections based on the determined level offading of the selected air-interface connection being less than thedetermined level of fading of the other of the first and secondair-interface connections and (ii) based on the selecting, establishingas the split ratio a split ratio that will put a majority of the dataflow of the UE on the identified air-interface connection.

FIG. 5 is next a flow chart depicting an example method that could becarried out in accordance with the present disclosure to control uplinkcommunication from a UE when the UE has at least two co-existingair-interface connections including a first air-interface connectionwith a first access node and a second air-interface connection with asecond access node, where one of the first and second air-interfaceconnections defines a primary uplink path of the UE to which the UErestricts uplink user-plane transmission from the UE unless and until atrigger condition causes the UE to split the uplink user-planetransmission between the first and second air-interface connections.

As shown in FIG. 5 , at block 60, the method includes comparing a levelof fading of the first air-interface connection with a level of fadingof the second air-interface connection. At block 62, the method thenincludes selecting, based at least on the comparing, one of the firstand second air-interface connections to be the primary uplink path ofthe UE. And at block 64, the method includes causing the UE to operatein accordance with the selecting.

In line with the discussion above, this method could be carried out by agiven one of the access nodes. And the act of causing the UE to operatein accordance with the selecting could involve transmitting from thegiven access node to the UE a directive that causes the UE to use theselected air-interface connection as the primary uplink path of the UE.

Further, as discussed above, the act of selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE could involve (i) determining, basedon the comparing, that the level of fading of the first air-interfaceconnection is less than the level of fading of the second access nodeand (ii) based at least on the determining, selecting the firstair-interface connection to be the primary uplink path of the UE.

In addition, as discussed above, the method as so defined could alsoinvolve (i) determining the level of fading of the first air-interfaceconnection based on fading experienced in one or more cells on which thefirst air-interface connection is defined and (ii) determining the levelof fading of the second air-interface connection based on fadingexperienced in one or more cells on which the second air-interfaceconnection is defined. And in that case, the act of comparing the levelof fading of the first air-interface connection with the level of fadingof the second air-interface connection could likewise involve comparingthe determined level of fading of the first air-interface connectionwith the determined level of fading of the second air-interfaceconnection.

Various other features discussed herein can be implemented in thiscontext as well, and vice versa.

Controlling the UE's Data Split Based on Per-Connection Insertion Loss

Yet another basis that the 4G eNB 12 could use for this dynamic controlis a comparison of insertion loss as to the cells on which UE isconnected respectively with the 4G eNB 12 and with the 5G gNB 14.

Insertion loss per cell could define a loss in signal power resultingfrom the insertion of one or more devices in a transmission path servingcommunication in the cell. For instance, on a per-cell basis orgenerally, an access node could be configured with one or more RFfilters, combiners, diplexers, triplexers, antenna ports, antennas,jumper cables, and other components that may cooperatively introducesignal loss of communications on the carrier. Further, if the accessnode is configured to provide service on multiple carriers, thesecomponents may introduce different levels of insertion loss as todifferent carriers, and/or different subsets of components may handlecommunications for different carriers and introduce different levels ofinsertion loss than each other. Insertion loss is undesirable, as itcould degrade communication between the access node and the UE, whichcould result in retransmissions and overall lower throughput.

Accordingly, the 4G eNB 12 could determine insertion loss of the UE's 4Gconnection as or otherwise based on insertion loss at the 4G eNB 14 asto the one or more 4G cells on which the UE is connected with the 4G eNB12, and the 4G eNB 12 could determine insertion loss of the UE's 5Gconnection as or otherwise based on insertion loss at the 5G gNB 14 asto the one or more 5G cells on which the UE is connected with the 5G gNB14. The 4G eNB 12 could then compare the determined insertion loss ofthe UE's 4G connection with the determined insertion loss of the UE's 5Gconnection. And based at least on that comparison, the 4G eNB 12 coulddetermine and set a split ratio for the UE.

For instance, based at least on this comparison, the 4G eNB 12 could seta split ratio that puts a majority of the UE's data flow on the UE'sconnection that has the lowest determined insertion loss, perhapssetting the split ratio to be equal to or otherwise based on an inverseof a ratio of the connections' respective determined levels of insertionloss. For example, if the determined insertion loss of the UE's 5Gconnection is twice that of the UE's 4G connection, then the 4G eNB 12could set a split ratio that puts half as much of the UE's data flow onthe UE's 5G connection as on the UE's 4G connection. Further,particularly if insertion loss would vary for downlink versus uplink,the 4G eNB 12 could carry out this process separately for the UE'sdownlink data flow based on a comparison of determined levels ofinsertion loss of the downlinks of the UE's connections, and for theUE's uplink data flow based on a comparison of determined levels ofinsertion loss of the uplinks of the UE's connections.

In addition or as part of this process, based at least on theinsertion-loss comparison, the 4G eNB 12 could also select and set oneof the UE's connections as the UE's primary uplink path, such as byselecting and setting as the UE's primary uplink path the connectionthat has the lowest determined insertion loss.

To facilitate this process, the 4G eNB 12 could be provisioned inadvance with a specification of the insertion loss respectively of eachcell on which the 4G eNB 12 provides service and also a specification ofinsertion loss respectively of each cell on which the 5G gNB 14 providesservice, or the 4G eNB 12 could otherwise have access to thatinformation. Engineering personnel and/or an automated system couldmeasure this insertion loss respectively per cell at the time each cellis deployed or configured for operation and could update themeasurements from time to time. The measured insertion loss could thenbe recorded in access-node profile data, to which the 4G eNB 12 couldhave access.

As noted above, at issue could be a comparison of (i) insertion loss ofthe 4G cell(s) on which the UE is connected with the 4G eNB 12 with (ii)insertion loss of the 5G cell(s) on which the UE is connected with the5G gNB 14, possibly limiting the downlink or uplink focus to just thosecells that would be used in practice for the UE's downlink or uplinkservice respectively. For instance, respectively for each of the UE'sconnections, the 4G eNB 12 could determine which cell(s) the UE isconnected and operating on, and the 4G eNB 12 could determine an averageor other rolled up measure of levels of insertion loss of the determinedcell(s). The 4G eNB 12 could then compare those determined levels ofinsertion loss of the UE's connections as a basis to set the UE's datasplit ratio and/or primary uplink path.

Further, as noted above, the 4G eNB 12 could consider additional factorsin this process as well.

FIG. 6 is a flow chart depicting an example method that could be carriedout in accordance with the present disclosure to control data split of aUE when the UE has at least two co-existing air-interface connectionsincluding a first air-interface connection with a first access node anda second air-interface connection with a second access node. Asdiscussed above, this method could be carried out by a computing system,such as by at least one of the two access nodes for instance.

As shown in FIG. 6 , at block 66, the example method includes comparinga level of insertion loss of the first air-interface connection with alevel of insertion loss of the second air-interface connection. At block68, the method then includes, based at least on the comparing,establishing a split ratio defining a distribution of data flow of theUE between at least the first air-interface connection and the secondair-interface connection. And at block 70, the method includes, based onthe establishing, causing the established split ratio to be applied.

In line with the discussion above, the split ratio at issue in thismethod could be an uplink split ratio and/or a downlink split ratio.Further, if the split ratio is an uplink split ratio, the act of causingthe established split ratio to be applied could involve transmitting tothe UE a directive that causes the UE to apply the established splitratio. And if the split ratio is a downlink split ratio, in a scenariowhere an entity splits the downlink data flow of the UE between thefirst and second connections, the act of causing the established splitratio to be applied could involve causing the entity to apply theestablished downlink split ratio.

As further discussed above, the method could additionally include (i)determining the level of insertion loss of the first air-interfaceconnection based on insertion loss at the first access node as to one ormore cells on which the first air-interface connection is defined and(ii) determining the level of insertion loss of the second air-interfaceconnection based on insertion loss at the second access node as to oneor more cells on which the second air-interface connection is defined.And the act of comparing the level of insertion loss of the firstair-interface connection with the level of insertion loss of the secondair-interface connection could involve comparing the determined level ofinsertion loss of the first air-interface connection with the determinedlevel of insertion loss of the second air-interface connection.

Further, the act of establishing the split ratio based on the comparingof the determined level of insertion loss of the first air-interfaceconnection with the determined level of insertion loss of the secondair-interface connection could involve establishing the split ratiobased on an inverse of a ratio of (i) the determined level of insertionloss of the first air-interface connection to (ii) the determined levelof insertion loss of the second air-interface connection. For instance,this could involve setting the split ratio to be equal to the inverse ofthe ratio of (i) the determined level of insertion loss of the firstair-interface connection to (ii) the determined level of insertion lossof the second air-interface connection.

Still further, the act of establishing the split ratio based on thecomparing of the determined level of insertion loss of the firstair-interface connection with the determined level of insertion loss ofthe second air-interface connection could involve (i) selecting one ofthe first and second air-interface connections based on the determinedlevel of insertion loss of the selected air-interface connection beingless than the determined level of insertion loss of the other of thefirst and second air-interface connections and (ii) based on theselecting, establishing as the split ratio a split ratio that will put amajority of the data flow of the UE on the identified air-interfaceconnection.

FIG. 7 is next a flow chart depicting an example method that could becarried out in accordance with the present disclosure to control uplinkcommunication from a UE when the UE has at least two co-existingair-interface connections including a first air-interface connectionwith a first access node and a second air-interface connection with asecond access node, where one of the first and second air-interfaceconnections defines a primary uplink path of the UE to which the UErestricts uplink user-plane transmission from the UE unless and until atrigger condition causes the UE to split the uplink user-planetransmission between the first and second air-interface connections.

As shown in FIG. 7 , at block 72, the method includes comparing a levelof insertion loss of the first air-interface connection with a level ofinsertion loss of the second air-interface connection. At block 74, themethod then includes selecting, based at least on the comparing, one ofthe first and second air-interface connections to be the primary uplinkpath of the UE. And at block 76, the method includes causing the UE tooperate in accordance with the selecting.

In line with the discussion above, this method could be carried out by agiven one of the access nodes. And the act of causing the UE to operatein accordance with the selecting could involve transmitting from thegiven access node to the UE a directive that causes the UE to use theselected air-interface connection as the primary uplink path of the UE.

Further, as discussed above, the act of selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE could involve (i) determining, basedon the comparing, that the level of insertion loss of the firstair-interface connection is less than the level of insertion loss of thesecond access node and (ii) based at least on the determining, selectingthe first air-interface connection to be the primary uplink path of theUE.

In addition, as discussed above, the method as so defined could alsoinvolve (i) determining the level of insertion loss of the firstair-interface connection based on insertion loss at the first accessnode as to one or more cells on which the first air-interface connectionis defined and (ii) determining the level of insertion loss of thesecond air-interface connection based on insertion loss at the secondaccess node as to one or more cells on which the second air-interfaceconnection is defined. And in that case, the act of comparing the levelof insertion loss of the first air-interface connection with the levelof insertion loss of the second air-interface connection could likewiseinvolve comparing the determined level of insertion loss of the firstair-interface connection with the determined level of insertion loss ofthe second air-interface connection.

Various other features discussed herein can be implemented in thiscontext as well, and vice versa.

Controlling the UE's Data Split Based on Per-Connection BeamformingSupport

Still another basis for that the 4G eNB 12 could use for this dynamiccontrol is a comparison of beamforming support on the UE's 4G connectionwith beamforming support on the UE's 5G connection.

Beamforming involves an access node focusing a targeted beam ofelectromagnetic energy specifically to the UE, as compared with theaccess node radiating generally throughout the access node's area ofcoverage. For instance, an access node might beamform to a UE byimplementing an antenna array that has multiple antenna elements andprogrammatically setting the phase and amplitude respectively of variousantenna elements so that transmissions from the antenna elementsconstructively or destructively combine to produce a beam in thedirection of the UE. Beamforming to a UE could thereby help to improvethe access node's antenna gain and associated transmission quality andthroughput experienced by the UE, and could help to reduce interferenceto other UEs, which may lead to overall improved resource availabilityand other benefits.

In practice, different cells on which a UE is served may have differentlevels of beamforming support than each other, based on various factorssuch as differences in physical access-node equipment (e.g., antennaelements) and/or differences in program logic per cell, as well asdifferences per band, RAT, or other aspect of UE support for suchbeamforming, among other possibilities. By way of example, one cell maysupport beamforming to the UE, but another cell may not supportbeamforming to the UE. As another example, one cell may support bothsingle-beam beamforming to the UE and more robust dual-beam beamformingto the UE, but the another cell may support just single-beam beamformingto the UE. And as yet another example, one cell may support beamformingto the UE with up to a high degree of accuracy to provide more powerfuland robust communication, but another cell may support beamforming withjust a lower level of accuracy (e.g., with a less narrow beam).

While the level of beamforming support per cell may not be a measurementper se, it could be quantified. For instance, the level of beamformingsupport per cell could be represented as a binary, Boolean valueindicating whether or not the cell supports beamforming to the UE, suchas by assigning a value of 1 (one) to a cell that supports beamformingand assigning a value of 0 (zero) to a cell that does not supportbeamforming to the UE. Further, the level of beamforming support percell could be more granularly quantified as well. For instance, a cell'slevel of beamforming support could be represented by a weighted scorebased on positive factors such as (i) the cell supporting beamforming tothe UE, (ii) the cell supporting dual-beam beamforming to the UE, (iii)the narrowness of beamforming supported by the cell, among otherpossibilities, with weights being a matter of engineering design choice,and (iv) the extent to which the UE supports the beamforming.

Accordingly, the 4G eNB 12 could determine a level of beamformingsupport of the UE's 4G connection as or otherwise based on beamformingsupport of the one or more 4G cells on which the UE is connected withthe 4G eNB 12, and the 4G eNB 12 could determine a level of beamformingsupport of the UE's 5G connection as or otherwise based on beamformingsupport of the one or more 5G cells on which the UE is connected withthe 5G gNB 14. The 4G eNB 12 could then compare the determined level ofbeamforming support of the UE's 4G connection with the determined levelof beamforming support of the UE's 5G connection. And based at least onthat comparison, the 4G eNB 12 could determine and set a split ratio forthe UE.

For instance, based at least on this comparison, the 4G eNB 12 could seta split ratio that puts a majority of the UE's data flow on the UE'sconnection that has the highest determined level of beamforming support,perhaps setting the split ratio to be equal to or otherwise based onratio of the connections' respective determined levels of beamformingsupport. For example, if the determined beamforming support of the UE's5G connection is twice that of the UE's 4G connection, then the 4G eNB12 could set a split ratio that puts twice as much of the UE's data flowon the UE's 5G connection as on the UE's 4G connection. Further, as todownlink beamforming, the 4G eNB 12 could carry out this processspecifically for the UE's downlink data split. And if uplink beamformingis supported, the 4G eNB 12 may carry out an analogous process for theUE's uplink data split.

To facilitate this process, the 4G eNB 12 could determine respectivelevels of beamforming support of the UE's 4G connection and 5Gconnection, based on records of the levels of beamforming support and/orrecords that establish the levels of beamforming support. In practice,for instance, the 4G eNB 12 and 5G gNB 14 could each keep such recordsrespectively for each of the one or more cells on which they serve theUE, and the 5G gNB 14 could report such records to the 4G eNB 12.

As noted above, at issue could be a comparison of (i) beamformingsupport of the 4G cell(s) on which the UE is connected with the 4G eNB12 with (ii) beamforming support of the 5G cell(s) on which the UE isconnected with the 5G gNB 14. For instance, respectively for each of theUE's connections, the 4G eNB 12 could determine which cell(s) the UE isconnected and operating on, and the 4G eNB 12 could determine an averageor other rolled up measure of level of beamforming support of thedetermined cell(s). The 4G eNB 12 could then compare those determinedlevels of beamforming support of the UE's connections as a basis to setthe UE's data split ratio and/or primary uplink path.

Further, as noted above, the 4G eNB 12 could consider additional factorsin this process as well.

FIG. 8 is a flow chart depicting an example method that could be carriedout in accordance with the present disclosure to control data split of aUE when the UE has at least two co-existing air-interface connectionsincluding a first air-interface connection with a first access node anda second air-interface connection with a second access node. Asdiscussed above, this method could be carried out by a computing system,such as by at least one of the two access nodes for instance.

As shown in FIG. 8 , at block 78, the example method includes comparinga level of beamforming support of the first air-interface connectionwith a level of beamforming support of the second air-interfaceconnection. At block 80, the method then includes, based at least on thecomparing, establishing a split ratio defining a distribution of dataflow of the UE between at least the first air-interface connection andthe second air-interface connection. And at block 82, the methodincludes, based on the establishing, causing the established split ratioto be applied.

In line with the discussion above, the split ratio at issue in thismethod could be an uplink split ratio and/or a downlink split ratio.Further, if the split ratio is an uplink split ratio, the act of causingthe established split ratio to be applied could involve transmitting tothe UE a directive that causes the UE to apply the established splitratio. And if the split ratio is a downlink split ratio, in a scenariowhere an entity splits the downlink data flow of the UE between thefirst and second connections, the act of causing the established splitratio to be applied could involve causing the entity to apply theestablished downlink split ratio.

As further discussed above, the method could additionally include (i)determining the level of beamforming support of the first air-interfaceconnection based on beamforming support of one or more cells on whichthe first air-interface connection is defined and (ii) determining thelevel of beamforming support of the second air-interface connectionbased on beamforming support of one or more cells on which the secondair-interface connection is defined. And the act of comparing the levelof beamforming support of the first air-interface connection with thelevel of beamforming support of the second air-interface connectioncould involve comparing the determined level of beamforming support ofthe first air-interface connection with the determined level ofbeamforming support of the second air-interface connection.

Further, the act of establishing the split ratio based on the comparingof the determined level of beamforming support of the firstair-interface connection with the determined level of beamformingsupport of the second air-interface connection could involveestablishing the split ratio based on a ratio of (i) the determinedlevel of beamforming support of the first air-interface connection to(ii) the determined level of beamforming support of the secondair-interface connection. For instance, this could involve setting thesplit ratio to be equal to the ratio of (i) the determined level ofbeamforming support of the first air-interface connection to (ii) thedetermined level of beamforming support of the second air-interfaceconnection.

Still further, the act of establishing the split ratio based on thecomparing of the determined level of beamforming support of the firstair-interface connection with the determined level of beamformingsupport of the second air-interface connection could involve (i)selecting one of the first and second air-interface connections based onthe determined level of beamforming support of the selectedair-interface connection being higher than the determined level ofbeamforming support of the other of the first and second air-interfaceconnections and (ii) based on the selecting, establishing as the splitratio a split ratio that will put a majority of the data flow of the UEon the identified air-interface connection.

FIG. 9 is next a flow chart depicting an example method that could becarried out in accordance with the present disclosure to control uplinkcommunication from a UE when the UE has at least two co-existingair-interface connections including a first air-interface connectionwith a first access node and a second air-interface connection with asecond access node, where one of the first and second air-interfaceconnections defines a primary uplink path of the UE to which the UErestricts uplink user-plane transmission from the UE unless and until atrigger condition causes the UE to split the uplink user-planetransmission between the first and second air-interface connections.

As shown in FIG. 9 , at block 84, the method includes comparing a levelof beamforming support of the first air-interface connection with alevel of beamforming support of the second air-interface connection. Atblock 86, the method then includes selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE. And at block 88, the method includescausing the UE to operate in accordance with the selecting.

In line with the discussion above, this method could be carried out by agiven one of the access nodes. And the act of causing the UE to operatein accordance with the selecting could involve transmitting from thegiven access node to the UE a directive that causes the UE to use theselected air-interface connection as the primary uplink path of the UE.

Further, as discussed above, the act of selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE could involve (i) determining, basedon the comparing, that the level of beamforming support of the firstair-interface connection is greater than the level of beamformingsupport of the second access node and (ii) based at least on thedetermining, selecting the first air-interface connection to be theprimary uplink path of the UE.

In addition, as discussed above, the method as so defined could alsoinvolve (i) determining the level of beamforming support of the firstair-interface connection based on beamforming support of one or morecells on which the first air-interface connection is defined and (ii)determining the level of beamforming support of the second air-interfaceconnection based on beamforming support of one or more cells on whichthe second air-interface connection is defined. And in that case, theact of comparing the level of beamforming support of the firstair-interface connection with the level of beamforming support of thesecond air-interface connection could likewise involve comparing thedetermined level of beamforming support of the first air-interfaceconnection with the determined level of beamforming support of thesecond air-interface connection.

Various other features discussed herein can be implemented in thiscontext as well, and vice versa.

Controlling the UE's Data Split Based on Per-Connection MIMO Support

Yet further, another basis that the 4G eNB 12 could use for this dynamiccontrol is a comparison of MIMO support on the UE's 4G connection withMIMO support on the UE's 5G connection.

MIMO involves air-interface communication occurring concurrently onmultiple different RF propagation paths—e.g., multiple beams—between theaccess node and the UE, from multiple transmit-antennas at thetransmitting end (e.g., at the access node or UE) to multiplereceive-antennas at the receiving end (e.g., at the UE or the accessnode). For instance, with spatial multiplexing, when the transmittingend has data to transmit to the receiving end, the transmitting endcould multiplex the onto multiple antenna output ports and thus ontomultiple RF propagation paths possibly on the same PRBs as each other,with each propagation path being referred to as a MIMO “layer”. MIMOservice could thus be characterized by how many how many transmit andreceive antennas are used, for instance as 2×2 MIMO where both ends usetwo antennas or as 4×4 MIMO where both ends use 4 antennas.

A dual-connected UE's multiple connections may have different levels ofMIMO support, which could be defined as or otherwise based on a maximumnumber of MIMO layers on which the UE can be served on the connection.The maximum number of MIMO layers on which a UE can be served on aconnection could be based on various factors such as physical equipment(e.g., antenna-array size) and/or program logic at the serving accessnode and/or load issues. Further, the maximum number of supported MIMOlayers on which a UE can be served on a connection could also be basedon the UE's channel quality, perhaps as indicated by a rank-index (RI)report from the UE, and based on UE capability data defining a maximumnumber of supported MIMO layers, among other possibilities.

Accordingly, the 4G eNB 12 could determine a level of MIMO support ofthe UE's 4G connection as or otherwise based on the maximum number ofMIMO layers on which the UE can be served on the 4G connection, and the4G eNB 12 could determine a level of MIMO support of the UE's 5Gconnection as or otherwise based on the maximum number of MIMO layers onwhich the UE can be served on the 5G connection. The 4G eNB 12 couldthen compare the determined level of MIMO support of the UE's 4Gconnection with the determined level of MIMO support of the UE's 5Gconnection. And based at least on that comparison, the 4G eNB 12 coulddetermine and set a split ratio for the UE.

For instance, based at least on this comparison, the 4G eNB 12 could seta split ratio that puts a majority of the UE's data flow on the UE'sconnection that has the highest determined level of MIMO support,perhaps setting the split ratio to be equal to or otherwise based on aratio of the connections' respective determined levels of MIMO support.For example, if the determined level of MIMO support of the UE's 5Gconnection is twice that of the UE's 4G connection, then the 4G eNB 12could set a split ratio that puts twice as much of the UE's data flow onthe UE's 5G connection as on the UE's 4G connection. Further, the 4G eNB12 could carry out this process separately for the UE's downlink dataflow based on a comparison of determined MIMO support as to thedownlinks of the UE's connections, and for the UE's uplink data flowbased on a comparison of determined MIMO support as to the uplinks ofthe UE's connections.

In addition or as part of this process, based at least on theMIMO-support comparison, the 4G eNB 12 could also select and set one ofthe UE's connections as the UE's primary uplink path, such as byselecting and setting as the UE's primary uplink path the connectionthat has the highest determined level of MIMO support.

To facilitate this process, the 4G eNB 12 could determine respectivelevels of MIMO support of the UE's 4G connection and 5G connection,based on records of the levels MIMO support and/or records thatestablish the levels of MIMO support. In practice, for instance, the 4GeNB 12 and 5G gNB 14 could each keep a record of the maximum number ofMIMO layers on which the UE can be served on their respective connectionwith the UE, based on factors such as those noted above, among otherpossibilities. And the 5G gNB 14 could report such records to the 4G eNB12. Alternatively or additionally, the EMS 36 could track the UE'sper-connection level of MIMO support and could report the levels of MIMOsupport to the 4G eNB 12, among other possibilities. The 4G eNB 12 couldthen compare those determined levels of MIMO support of the UE'sconnections as a basis to set the UE's data split ratio and/or primaryuplink path.

Further, as noted above, the 4G eNB 12 could consider additional factorsin this process as well.

FIG. 10 is a flow chart depicting an example method that could becarried out in accordance with the present disclosure to control datasplit of a UE when the UE has at least two co-existing air-interfaceconnections including a first air-interface connection with a firstaccess node and a second air-interface connection with a second accessnode. As discussed above, this method could be carried out by acomputing system, such as by at least one of the two access nodes forinstance.

As shown in FIG. 10 , at block 90, the example method includes comparinga level of MIMO support of the first air-interface connection with alevel of MIMO support of the second air-interface connection. At block92, the method then includes, based at least on the comparing,establishing a split ratio defining a distribution of data flow of theUE between at least the first air-interface connection and the secondair-interface connection. And at block 94, the method includes, based onthe establishing, causing the established split ratio to be applied.

In line with the discussion above, the split ratio at issue in thismethod could be an uplink split ratio and/or a downlink split ratio.Further, if the split ratio is an uplink split ratio, the act of causingthe established split ratio to be applied could involve transmitting tothe UE a directive that causes the UE to apply the established splitratio. And if the split ratio is a downlink split ratio, in a scenariowhere an entity splits the downlink data flow of the UE between thefirst and second connections, the act of causing the established splitratio to be applied could involve causing the entity to apply theestablished downlink split ratio.

As further discussed above, the method could additionally include (i)determining the level of MIMO support of the first air-interfaceconnection based on a maximum number of MIMO layers on which the UE canbe served on the first air-interface connection and (ii) determining thelevel of MIMO support of the second air-interface connection based on amaximum number of MIMO layers on which the UE can be served on thesecond air-interface connection. And the act of comparing the level ofMIMO support of the first air-interface connection with the level ofMIMO support of the second air-interface connection could involvecomparing the determined level of MIMO support of the firstair-interface connection with the determined level of MIMO support ofthe second air-interface connection.

Further, the act of establishing the split ratio based on the comparingof the determined level of MIMO support of the first air-interfaceconnection with the determined level of MIMO support of the secondair-interface connection could involve establishing the split ratiobased on a ratio of (i) the determined level of MIMO support of thefirst air-interface connection to (ii) the determined level of MIMOsupport of the second air-interface connection. For instance, this couldinvolve setting the split ratio to be equal to the ratio of (i) thedetermined level of MIMO support of the first air-interface connectionto (ii) the determined level of MIMO support of the second air-interfaceconnection.

Still further, the act of establishing the split ratio based on thecomparing of the determined level of MIMO support of the firstair-interface connection with the determined level of MIMO support ofthe second air-interface connection could involve (i) selecting one ofthe first and second air-interface connections based on the determinedlevel of MIMO support of the selected air-interface connection beinghigher than the determined level of MIMO support of the other of thefirst and second air-interface connections and (ii) based on theselecting, establishing as the split ratio a split ratio that will put amajority of the data flow of the UE on the identified air-interfaceconnection.

FIG. 11 is next a flow chart depicting an example method that could becarried out in accordance with the present disclosure to control uplinkcommunication from a UE when the UE has at least two co-existingair-interface connections including a first air-interface connectionwith a first access node and a second air-interface connection with asecond access node, where one of the first and second air-interfaceconnections defines a primary uplink path of the UE to which the UErestricts uplink user-plane transmission from the UE unless and until atrigger condition causes the UE to split the uplink user-planetransmission between the first and second air-interface connections.

As shown in FIG. 11 , at block 96, the method includes comparing a levelof MIMO support of the first air-interface connection with a level ofMIMO support of the second air-interface connection. At block 98, themethod then includes selecting, based at least on the comparing, one ofthe first and second air-interface connections to be the primary uplinkpath of the UE. And at block 100, the method includes causing the UE tooperate in accordance with the selecting.

In line with the discussion above, this method could be carried out by agiven one of the access nodes. And the act of causing the UE to operatein accordance with the selecting could involve transmitting from thegiven access node to the UE a directive that causes the UE to use theselected air-interface connection as the primary uplink path of the UE.

Further, as discussed above, the act of selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE could involve (i) determining, basedon the comparing, that the level of MIMO support of the firstair-interface connection is greater than the level of MIMO support ofthe second access node and (ii) based at least on the determining,selecting the first air-interface connection to be the primary uplinkpath of the UE.

In addition, as discussed above, the method as so defined could alsoinvolve (i) determining the level of MIMO support of the firstair-interface connection based on a maximum number of MIMO layers onwhich the UE can be served on the first air-interface connection and(ii) determining the level of MIMO support of the second air-interfaceconnection based on a maximum number of MIMO layers on which the UE canbe served on the second air-interface connection. And in that case, theact of comparing the level of MIMO support of the first air-interfaceconnection with the level of MIMO support of the second air-interfaceconnection could likewise involve comparing the determined level of MIMOsupport of the first air-interface connection with the determined levelof MIMO support of the second air-interface connection.

Various other features discussed herein can be implemented in thiscontext as well, and vice versa.

Controlling the UE's Data Split Based on Per-Connection FrequencyBandwidth

Still further, another basis that the 4G eNB 12 could use for thisdynamic control is a comparison of the aggregate frequency bandwidthrespectively of the UE's connections, evaluated as to downlink and/oruplink channel bandwidth.

Each of the UE's connections, defined on one or more cells, would havean aggregate frequency bandwidth as the total frequency bandwidth acrossthe one or more cells. For instance, if the UE is connected on just a 20MHz wide carrier, then the UE's aggregate frequency bandwidth of thatconnection may be 20 MHz. Whereas if the UE is connected on both a 20MHz carrier and a 15 MHz carrier, then the UE's aggregate frequencybandwidth of the connection may be 35 MHz. Variations and exclusionscould be applied as well. In general, the greater the aggregatefrequency bandwidth of a connection, the higher the UE's peak data ratecould be on that connection, which would be more desirable.

Accordingly, the 4G eNB 12 could determine the aggregate bandwidth ofthe UE's 4G connection, and the 4G eNB 12 could determine the aggregatebandwidth of the UE's 5G connection. The 4G eNB 12 could then comparethe determined aggregate bandwidth of the UE's 4G connection with thedetermined aggregate bandwidth of the UE's 5G connection. And based atleast on that comparison, the 4G eNB 12 could determine and set a splitratio for the UE.

For instance, based at least on this comparison, the 4G eNB 12 could seta split ratio that puts a majority of the UE's data flow on the UE'sconnection that has the greatest aggregate bandwidth, perhaps settingthe split ratio to be equal to or otherwise based on a ratio of theconnections' respective aggregate bandwidths. For example, if thedetermined aggregate bandwidth of the UE's 5G connection is twice thatof the UE's 4G connection, then the 4G eNB 12 could set a split ratiothat puts twice as much of the UE's data flow on the UE's 5G connectionas on the UE's 4G connection. Further, the 4G eNB 12 could carry outthis process separately for the UE's downlink data flow based on acomparison of determined aggregate bandwidths of the downlinks of theUE's connections, and for the UE's uplink data flow based on acomparison of determined aggregate bandwidths of the uplinks of the UE'sconnections.

In addition or as part of this process, based at least on theaggregate-bandwidth comparison, the 4G eNB 12 could also select and setone of the UE's connections as the UE's primary uplink path, such as byselecting and setting as the UE's primary uplink path the connectionthat has the greatest determined aggregate bandwidth.

To facilitate this process, the 4G eNB 12 could determine respectiveaggregate bandwidths of the UE's 4G connection and 5G connection, basedon records of the carriers and associated carrier bandwidths encompassedby each connection. For instance, the 4G eNB 12 may have stored in acontext record for the UE a record of the one or more 4G carriers onwhich the UE is connected with the 4G eNB 12 and of the frequencychannel bandwidth (e.g., downlink and/or uplink) respectively of eachsuch carrier. Further, the 4G eNB 12 may also have stored in thatcontext record and/or may determine through signaling with the 5G eNB 14a record of the one or more 5G carriers on which the UE is connectedwith the 5G gNB 14 and likewise of the frequency channel bandwidthrespectively of each such carrier. The 4G eNB 12 could thus refer tothose records to compute or otherwise determine the aggregate bandwidthof the UE's 4G connection and the aggregate bandwidth of the UE's 5Gconnection.

Further, as noted above, the 4G eNB 12 could consider additional factorsin this process as well.

FIG. 12 is a flow chart depicting an example method that could becarried out in accordance with the present disclosure to control datasplit of a UE when the UE has at least two co-existing air-interfaceconnections including a first air-interface connection with a firstaccess node and a second air-interface connection with a second accessnode. As discussed above, this method could be carried out by acomputing system, such as by at least one of the two access nodes forinstance.

As shown in FIG. 12 , at block 102, the example method includescomparing an aggregate frequency bandwidth of the first air-interfaceconnection with an aggregate frequency bandwidth aggregate frequencybandwidth of the second air-interface connection. At block 104, themethod then includes, based at least on the comparing, establishing asplit ratio defining a distribution of data flow of the UE between atleast the first air-interface connection and the second air-interfaceconnection. And at block 106, the method includes, based on theestablishing, causing the established split ratio to be applied.

In line with the discussion above, the split ratio at issue in thismethod could be an uplink split ratio and/or a downlink split ratio.Further, if the split ratio is an uplink split ratio, the act of causingthe established split ratio to be applied could involve transmitting tothe UE a directive that causes the UE to apply the established splitratio. And if the split ratio is a downlink split ratio, in a scenariowhere an entity splits the downlink data flow of the UE between thefirst and second connections, the act of causing the established splitratio to be applied could involve causing the entity to apply theestablished downlink split ratio.

As further discussed above, the method could additionally includedetermining the aggregate frequency bandwidth of the first air-interfaceconnection and determining the aggregate frequency bandwidth of thesecond air-interface connection. And the act of comparing the aggregatefrequency bandwidth of the first air-interface connection with theaggregate frequency bandwidth of the second air-interface connectioncould involve comparing the determined aggregate frequency bandwidth ofthe first air-interface connection with the determined aggregatefrequency bandwidth of the second air-interface connection.

Further, the act of establishing the split ratio based on the comparingof the determined aggregate frequency bandwidth of the firstair-interface connection with the determined aggregate frequencybandwidth of the second air-interface connection could involveestablishing the split ratio based on a ratio of (i) the determinedaggregate frequency bandwidth of the first air-interface connection to(ii) the determined aggregate frequency bandwidth of the secondair-interface connection. For instance, this could involve setting thesplit ratio to be equal to the ratio of (i) the determined aggregatefrequency bandwidth of the first air-interface connection to (ii) thedetermined aggregate frequency bandwidth of the second air-interfaceconnection.

Still further, the act of establishing the split ratio based on thecomparing of the determined aggregate frequency bandwidth of the firstair-interface connection with the determined aggregate frequencybandwidth of the second air-interface connection could involve (i)selecting one of the first and second air-interface connections based onthe determined aggregate frequency bandwidth of the selectedair-interface connection being greater than the determined aggregatefrequency bandwidth of the other of the first and second air-interfaceconnections and (ii) based on the selecting, establishing as the splitratio a split ratio that will put a majority of the data flow of the UEon the identified air-interface connection.

FIG. 13 is next a flow chart depicting an example method that could becarried out in accordance with the present disclosure to control uplinkcommunication from a UE when the UE has at least two co-existingair-interface connections including a first air-interface connectionwith a first access node and a second air-interface connection with asecond access node, where one of the first and second air-interfaceconnections defines a primary uplink path of the UE to which the UErestricts uplink user-plane transmission from the UE unless and until atrigger condition causes the UE to split the uplink user-planetransmission between the first and second air-interface connections.

As shown in FIG. 13 , at block 108, the method includes comparing anaggregate frequency bandwidth of the first air-interface connection withan aggregate frequency bandwidth of the second air-interface connection.At block 110, the method then includes selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE. And at block 112, the method includescausing the UE to operate in accordance with the selecting.

In line with the discussion above, this method could be carried out by agiven one of the access nodes. And the act of causing the UE to operatein accordance with the selecting could involve transmitting from thegiven access node to the UE a directive that causes the UE to use theselected air-interface connection as the primary uplink path of the UE.

Further, as discussed above, the act of selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE could involve (i) determining, basedon the comparing, that the aggregate frequency bandwidth of the firstair-interface connection is greater than the aggregate frequencybandwidth of the second access node and (ii) based at least on thedetermining, selecting the first air-interface connection to be theprimary uplink path of the UE.

In addition, as discussed above, the method as so defined could alsoinvolve determining the aggregate frequency bandwidth of the firstair-interface connection and determining the aggregate frequencybandwidth of the second air-interface connection. And in that case, theact of comparing the aggregate frequency bandwidth of the firstair-interface connection with the aggregate frequency bandwidth of thesecond air-interface connection could likewise involve comparing thedetermined aggregate frequency bandwidth of the first air-interfaceconnection with the determined aggregate frequency bandwidth of thesecond air-interface connection.

Various other features discussed herein can be implemented in thiscontext as well, and vice versa.

Example System Structure

FIG. 14 is a simplified block diagram of an example computing systemthat could be operable in accordance with the present disclosure. Asnoted above, such a computing system could be provided at one of theaccess nodes in the arrangement of FIG. 1 , among other possibilities.

As shown in FIG. 14 , the example computing system includes a networkcommunication interface 114, a processor 116, and non-transitory datastorage 118, which could be integrated together and/or interconnected bya system bus, network, or other connection mechanism 120.

The network communication interface 114 could comprise a physicalnetwork connector (e.g., an Ethernet interface) and associatedcommunication logic (e.g., protocol stacks) to facilitate wired orwireless network communication with various other entities. Theprocessor 116 could comprise one or more general purpose processors(e.g., microprocessors) and/or one or more specialized processors (e.g.,application specific integrated circuits). And the non-transitory datastorage 118 could comprise one or more volatile and/or non-volatilestorage components (e.g., magnetic, optical, or flash storage,necessarily non-transitory).

As shown, the data storage 118 could then store program instructions122, which could be executable by the processor 116 to cause thecomputing system to carry out various operations described herein,including but not limited to the operations discussed above in relationto one or more of FIGS. 2-13 .

Various other features discussed herein can be implemented in thiscontext as well, and vice versa.

FIG. 15 is a simplified block diagram of an example access node thatcould be operable in accordance with the present disclosure. This accessnode could represent the one of the access nodes described, such as the4G eNB 12 or the 5G gNB 14, among other possibilities.

As shown in FIG. 15 , the example access node includes a wirelesscommunication interface 124, a network communication interface 126, anda controller 128, which could be integrated together and/orcommunicatively linked together by a system bus, network, or otherconnection mechanism 130.

In an example implementation, the wireless communication interface 126could comprise an antenna structure, which could be tower mounted orcould take other forms, and associated components such as a poweramplifier and a wireless transceiver, so as to facilitate providing acell defining an air interface and engaging air-interface communicationon the air interface in accordance with an applicable RAT. And thenetwork communication interface 126 could comprise a physical networkconnector (e.g., an Ethernet interface) and associated communicationlogic (e.g., protocol stacks) to facilitate wired or wireless networkcommunication with various other entities, such as with other accessnodes and various core-network entities.

Further, the controller 128 (which might be provided by a baseband unitof the access node, for instance) could comprise a processor 132 (e.g.,one or more general purpose processors (e.g., microprocessors) and/orone or more specialized processors (e.g., application specificintegrated circuits)), non-transitory data storage 134 (e.g., one ormore volatile and/or non-volatile storage components (such as magnetic,optical, or flash storage), necessarily non-transitory), and programinstructions 136 stored in the non-transitory data storage andexecutable by processor to carry out various operations such as thosediscussed herein, including for example the operations discussed abovein relation to one or more of FIGS. 2-13 .

Various other features discussed herein can be implemented in thiscontext as well, and vice versa.

The present disclosure also contemplates at least one non-transitorycomputer readable medium having stored thereon (e.g., being encodedwith) program instructions executable by at least one processing unit tocarry out various operations described above.

Exemplary embodiments have been described above. Those skilled in theart will understand, however, that changes and modifications may be madeto these embodiments without departing from the true scope and spirit ofthe invention.

What is claimed is:
 1. A method for controlling uplink communicationfrom a user equipment device (UE) when the UE has at least twoco-existing air-interface connections including a first air-interfaceconnection with a first access node and a second air-interfaceconnection with a second access node, wherein one of the first andsecond air-interface connections defines a primary uplink path of the UEto which the UE restricts uplink user-plane transmission from the UEunless and until a trigger condition causes the UE to split the uplinkuser-plane transmission between the first and second air-interfaceconnections, the method comprising: comparing a maximum number ofmultiple-input-multiple-output (MIMO) layers of the first air-interfaceconnection with a maximum number of MIMO layers of the secondair-interface connection; selecting, based at least on the comparing,one of the first and second air-interface connections to be the primaryuplink path of the UE; and causing the UE to operate in accordance withthe selecting.
 2. The method of claim 1, wherein the method is carriedout by a given one of the first and second access nodes, and whereincausing the UE to operate in accordance with the selecting comprisestransmitting from the given access node to the UE a directive thatcauses the UE to use the selected air-interface connection as theprimary uplink path of the UE.
 3. The method of claim 2, whereintransmitting the directive to the UE comprises transmitting to the UE aRadio Resource Control (RRC) connection reconfiguration message definingthe directive.
 4. The method of claim 1, wherein selecting, based atleast on the comparing, one of the first and second air-interfaceconnections to be the primary uplink path of the UE comprises:determining, based on the comparing, that the maximum number of MIMOlayers of the first air-interface connection is greater than the maximumnumber of MIMO layers of the second air-interface connection; and basedat least on the determining, selecting the first air-interfaceconnection to be the primary uplink path of the UE.
 5. The method ofclaim 1, further comprising: determining the maximum number of MIMOlayers of the first air-interface connection based on a maximum numberof MIMO layers on which the UE can be served on the first air-interfaceconnection; and determining the maximum number of MIMO layers of thesecond air-interface connection based on a maximum number of MIMO layerson which the UE can be served on the second air-interface connection,wherein comparing the maximum number of MIMO layers of the firstair-interface connection with the maximum number of MIMO layers of thesecond air-interface connection comprises comparing the determinedmaximum number of MIMO layers of the first air-interface connection withthe determined maximum number of MIMO layers of the second air-interfaceconnection.
 6. The method of claim 1, wherein the first air-interfaceconnection operates in accordance with a first radio access technology(RAT) and the second air-interface connection operates in accordancewith a second RAT different than the first RAT.
 7. The method of claim1, further comprising: after selecting one of the first and secondair-interface connections to be the primary uplink path of the UE andcausing the UE to operate in accordance with the selecting, latercausing the other of the first and second air-interface connections tobe the primary uplink path of the UE.
 8. A computing system configuredto control uplink communication from a user equipment device (UE) whenthe UE has at least two co-existing air-interface connections includinga first air-interface connection with a first access node and a secondair-interface connection with a second access node, wherein one of thefirst and second air-interface connections defines a primary uplink pathof the UE to which the UE restricts uplink user-plane transmission fromthe UE unless and until a trigger condition causes the UE to split theuplink user-plane transmission between the first and secondair-interface connections, the computing system comprising: a processor;non-transitory data storage; and program instructions stored in thenon-transitory data storage and executable by the processor to cause thecomputing system to carry out operations including: comparing a maximumnumber of multiple-input-multiple-output (MIMO) layers of the firstair-interface connection with a maximum number of MIMO layers of thesecond air-interface connection, selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE, and causing the UE to operate inaccordance with the selecting.
 9. The computing system of claim 8,wherein the system is implemented at a given one of the first and secondaccess nodes, and wherein causing the UE to operate in accordance withthe selecting comprises transmitting from the given access node to theUE a directive that causes the UE to use the selected air-interfaceconnection as the primary uplink path of the UE.
 10. The computingsystem of claim 9, wherein transmitting the directive to the UEcomprises transmitting to the UE a Radio Resource Control (RRC)connection reconfiguration message defining the directive.
 11. Thecomputing system of claim 8, wherein selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE comprises: determining, based on thecomparing, that the maximum number of MIMO layers of the firstair-interface connection is greater than the maximum number of MIMOlayers of the second air-interface connection; and based at least on thedetermining, selecting the first air-interface connection to be theprimary uplink path of the UE.
 12. The computing system of claim 8,wherein the operations further include: determining the maximum numberof MIMO layers of the first air-interface connection based on a maximumnumber of MIMO layers on which the UE can be served on the firstair-interface connection; and determining the maximum number of MIMOlayers of the second air-interface connection based on a maximum numberof MIMO layers on which the UE can be served on the second air-interfaceconnection, wherein comparing the maximum number of MIMO layers of thefirst air-interface connection with the maximum number of MIMO layers ofthe second air-interface connection comprises comparing the determinedmaximum number of MIMO layers of the first air-interface connection withthe determined maximum number of MIMO layers of the second air-interfaceconnection.
 13. The computing system of claim 8, wherein the firstair-interface connection operates in accordance with a first radioaccess technology (RAT) and the second air-interface connection operatesin accordance with a second RAT different than the first RAT.
 14. Thecomputing system of claim 8, wherein the operations further include:after selecting one of the first and second air-interface connections tobe the primary uplink path of the UE and causing the UE to operate inaccordance with the selecting, later causing the other of the first andsecond air-interface connections to be the primary uplink path of theUE.
 15. At least one non-transitory computer-readable medium havingstored thereon program instructions executable by at least oneprocessing unit to carry out operations for controlling uplinkcommunication from a user equipment device (UE) when the UE has at leasttwo co-existing air-interface connections including a firstair-interface connection with a first access node and a secondair-interface connection with a second access node, wherein one of thefirst and second air-interface connections defines a primary uplink pathof the UE to which the UE restricts uplink user-plane transmission fromthe UE unless and until a trigger condition causes the UE to split theuplink user-plane transmission between the first and secondair-interface connections, the operations comprising: comparing amaximum number of multiple-input-multiple-output (MIMO) layers of thefirst air-interface connection with a maximum number of MIMO layers ofthe second air-interface connection; selecting, based at least on thecomparing, one of the first and second air-interface connections to bethe primary uplink path of the UE; and causing the UE to operate inaccordance with the selecting.
 16. The at least one non-transitorycomputer-readable medium of claim 15, wherein causing the UE to operatein accordance with the selecting comprises transmitting to the UE adirective that causes the UE to use the selected air-interfaceconnection as the primary uplink path of the UE, wherein transmittingthe directive to the UE comprises transmitting to the UE a RadioResource Control (RRC) connection reconfiguration message defining thedirective.
 17. The at least one non-transitory computer-readable mediumof claim 15, wherein selecting, based at least on the comparing, one ofthe first and second air-interface connections to be the primary uplinkpath of the UE comprises: determining, based on the comparing, that themaximum number of MIMO layers of the first air-interface connection isgreater than the maximum number of MIMO layers of the secondair-interface connection; and based at least on the determining,selecting the first air-interface connection to be the primary uplinkpath of the UE.
 18. The at least one non-transitory computer-readablemedium of claim 15, wherein the operations further comprise: determiningthe maximum number of MIMO layers of the first air-interface connectionbased on a maximum number of MIMO layers on which the UE can be servedon the first air-interface connection; and determining the maximumnumber of MIMO layers of the second air-interface connection based on amaximum number of MIMO layers on which the UE can be served on thesecond air-interface connection, wherein comparing the maximum number ofMIMO layers of the first air-interface connection with the maximumnumber of MIMO layers of the second air-interface connection comprisescomparing the determined maximum number of MIMO layers of the firstair-interface connection with the determined maximum number of MIMOlayers of the second air-interface connection.
 19. The at least onenon-transitory computer-readable medium of claim 15, wherein the firstair-interface connection operates in accordance with a first radioaccess technology (RAT) and the second air-interface connection operatesin accordance with a second RAT different than the first RAT.
 20. The atleast one non-transitory computer-readable medium of claim 15, whereinthe operations further comprise: after selecting one of the first andsecond air-interface connections to be the primary uplink path of the UEand causing the UE to operate in accordance with the selecting, latercausing the other of the first and second air-interface connections tobe the primary uplink path of the UE.